Viscous Dissipation of Polymer Melt in Micro Channels and Macro Channels

2014 ◽  
Vol 609-610 ◽  
pp. 521-525
Author(s):  
Bin Xu ◽  
Xiao Yu An ◽  
Liang Chao Li ◽  
Guang Ming Li

Viscous dissipation is the key factor impacting flowing characteristics of polymer melt. In order to study the difference between micro scale and macro scale, experimental studies of viscous dissipation at various shear rate were investigated with several polymers, including PMMA and HDPE, at different temperature when melts flow through 1000μm,500μm,350μm diameter channels of identical aspects ratio in the paper. The results indicate that the temperature rises caused by viscous dissipation increase with increasing shear rate and the temperature rise for some shear rate decreases with increasing melts temperature. The temperature rises decrease significantly with the reduction of the characteristic size of micro channel at the same shear rate. However, the average temperature rises per unit length increase when the character size of channel decreases. This indicates the shear friction gradually increases with the decrease of channel characteristic size. Therefore polymer melt viscous dissipation effects of micro scale dimensions are different from that of macro-scale dimensions.

2011 ◽  
Vol 314-316 ◽  
pp. 1346-1349
Author(s):  
Bin Xu ◽  
Yu Bin Lu ◽  
Guang Ming Li ◽  
Song Xue

Experimental observations indicate that the viscosity of polymer melt flowing through micro channel is altered with variation of characteristic size of micro channels. The explanation about the trend of various viscosity is inconsistent. In this paper, the micro channel dies of 1000μm ,500μm and 350μm diameter were developed and with several polymers, including PP , PS and HDPE, depending on the capillary flow model, the measurement experiments of polymer melt viscosity were investigated at various shear rate. Test results show that with micro-channel size decrease, the percentage reduction in viscosity increases and the difference of viscosities in different micro channels reduces with increasing shear rate.


2010 ◽  
Vol 97-101 ◽  
pp. 2527-2532 ◽  
Author(s):  
Tong Min Yu ◽  
Hai Xin Bei ◽  
Ze Yu Yan ◽  
Bin Xu ◽  
Hua Xu ◽  
...  

The polymer melts viscous dissipation effects of micro scale dimensions are different from that of macro-scale dimensions. In this paper, the temperature rises due to viscous dissipation were investigated when amorphous polymer material, PMMA, flows through several micro-channels with the diameters of 350μm, 500μm and different aspect ratios. The results indicate that, temperature rises reduce with the increase of inlet temperature of melt and increase with increasing channel’s diameter and aspect ratio at the same shear rate. The outlet temperature rises due to viscous dissipation in all micro channels increase with the increase of shear rate. In addition, the outlet temperature rise grows faster with the decrease of micro-channel’s diameter. Therefore, viscous dissipation effect is significant and should not be neglected in micro channel.


Author(s):  
N. La Forgia ◽  
M. Fernandino ◽  
C. A. Dorao

Compact and efficient heat exchangers are needed to obtain energy efficient processes. An optimal design and operation of such systems require improving the physical understanding of the complex two-phase flow phenomena. The complexity of the evaporation process has been widely acknowledged, and several descriptions have been proposed with special focus on the micro region between the bubble interface and the heated wall [1,2,3]. In the case of evaporation in micro channels and as a consequence of the large interfacial area to volume ratio, some factors such as surface tension, frictional pressure drop, nucleation, etc. are playing an important role, and thus cannot be neglected. The prediction of the behavior of micro-scale two-phase evaporation is still limited. While experimental studies [4] have provided valuable insight of the phenomena, due to limitations in the experimental conditions all aspects of the micro scale boiling flow are not completely understood. In this sense, a computational approach can help to complement experimental studies. However the simulation of micro scale flow has several challenging aspects such as the tracking of the bubble interface, introduction of the surface tension effects, subscale modeling of the micro region, and the like. The goal of this work is to discuss the development of a computational model for studying micro scale evaporation phenomena and bubble dynamics in micro scale boiling and flowing. The model is based on a continuum surface force (CSF) model which belongs to the family of diffuse interface methods. A particular aspect of this work is the subgrid modeling of the micro scale region and its coupling to the macro scale flow. The mathematical model is solved using a spectral element method which provides a good balance between accuracy and computational cost.


2011 ◽  
Vol 189-193 ◽  
pp. 451-454 ◽  
Author(s):  
Bin Xu ◽  
Yu Bin Lu ◽  
Guang Ming Li ◽  
Song Xue ◽  
Bei Ping Xiang

With the rapid development of micro injection molding, the determination of melt rheological behavior within micro mold cavity is very important for the accurate simulation modeling. Yet several investigations show the viscosity of melt decreases with the reduction of micro channel characteristic size, but there has been no sufficient experimental data for the conclusion. In this paper, depending on the capillary flow model, the measurement experiments of polymer melt viscosity were investigated when Polymethyl Methacrylate (PMMA) was extruded through the micro channel dies of 1000μm ,500μm and 350μm diameter. Test results show that, as micro-channel size decreases, the viscosity increases and the difference of viscosities in different micro channels reduces with increasing shear rate. This indicates microscopic scale melt rheological behavior of PMMA is different from that of other materials.


2013 ◽  
Vol 33 (2) ◽  
pp. 95-110
Author(s):  
Mustafa Tutar ◽  
Ali Karakus

Abstract The combined effects of solidification and viscous dissipation on the hydrodynamic and thermal behavior of polymer melt flow during the injection process in a straight plane channel of constant cross section are numerically studied by considering the shear-rate and temperature-dependent viscosity and transient-phase change behavior. A numerical finite volume method, in conjunction with a modified form of the Cross constitutive equation to account for shear rate, temperature-dependent viscosity changes and a slightly modified form of the method proposed by Voller and Prakash to account for solidification of the liquid phase, is used and a validation with an analytical solution is presented for viscous heating effects. The hydrodynamic and solidified layers growth under the influence of a transient phase-change process and viscous dissipation, are analyzed for a commercial polymer melt flow, polypropylene (PP) for different parametric conditions namely, inflow velocity, polymer injection (inflow) temperature, the channel wall temperature, and the channel height. The results demonstrate that the proposed numerical formulations, including conjugate effects of viscous heating and transient-solidification on the present thermal transport process, can provide an accurate and realistic representation of polymer melt flow behavior during the injection molding process in plane channels with less simplifying assumptions.


2010 ◽  
Vol 24 (7) ◽  
pp. 1417-1423 ◽  
Author(s):  
Bin Xu ◽  
Minjie Wang ◽  
Tongmin Yu ◽  
Danyang Zhao

Polymers ◽  
2021 ◽  
Vol 13 (24) ◽  
pp. 4451
Author(s):  
Wangqing Wu ◽  
Ke Zeng ◽  
Baishun Zhao ◽  
Fengnan Duan ◽  
Fengze Jiang

Capillary rheometers have been widely used for the rheological measurement of polymer melts. However, when micro capillary dies are used, the results are usually neither accurate nor consistent, even under the same measurement conditions. In this work, theoretical modeling and experimental studies were conducted for a more profound understanding of the mechanism by which the initial and boundary conditions influence the inaccuracy in the apparent shear viscosity determination with micro capillary dies (diameters: 500 μm, 200 μm, 100 μm). The results indicate that the amount of polymer initially in the barrel, the pre-compaction pressure and the capillary die diameter have a significant influence on the development of the micro scale inlet pressure, which directly determines the accuracy of the measurement at low and medium shear rates. The varying melt compressibility was confirmed to be the main factor directly related to the inaccuracy in the micro scale apparent shear viscosity determination. It is suggested that measures such as reducing the amount of polymer initially in the barrel and increasing the pre-compaction pressure could be used to reduce the measurement inaccuracy.


2017 ◽  
pp. 5-8
Author(s):  
Wojciech Sajkowski

Introduction to the Thematic SectionThe images of the borders of civilizations is the main topic of the thematic section of this issue of Colloquia Humanistica. In the call for papers it was emphasised, that this issue is particularly important, because the notion of civilization is strictly related to the issue of borders since it would became meaningless without the opposition to another civilization, or the lack of it. The juxtaposition between the notion of civilization and its different antinomies seems easier to display when seen from its centre, however the shape of its border is not always clear, even if it has a foundation in clear geographical or political divisions. Thus, this border can be represented as a linear frontier between a civilized state and barbaric lands, or as a borderland which encompasses some kind of fluent transition. The civilization border can be also represented in a macro scale, shaping geographic divisions of the continents (as it was in the case of the Balkans), but its depiction can also concern the micro scale, for example the difference between an urban and a natural landscape. The notion is even broader, because it is not only treated in the context of space but also social behaviours and their evolution (which is bound with notion of the progress since the Enlightenment). The question establishing the difference between the civilized and the uncivilized is still shaping the identity of modern societies, and thus it is worth attention. Wprowadzenie do sekcji tematycznejTematem przewodnim szóstego numeru rocznika Colloquia Humanistica są obrazy granic cywilizacji. Temat ten wydaje się niezwykle istotny, ponieważ pojęcie cywilizacji ściśle wiąże się z kategorią granicy, skoro traci ono znaczenie, gdy nie zachodzi opozycja wobec innej cywilizacji. Zestawienie pojęcia cywilizacji i jego różnych antynomii najłatwiej przejawia się, jak się wydaje, z perspektywy centrum, jednakże kształt jej granic nie zawsze rysuje się wyraźnie, nawet gdy wywodzi się ona z jasnych podziałów geograficznych czy politycznych. Granicę może zatem reprezentować linia między cywilizowanym państwem a krajami barbarzyńskimi lub też pogranicze, stanowiące coś w rodzaju płynnego przejścia. Granicę cywilizacji można też przedstawić w makroskali poprzez podziały geograficzne na kontynencie (jak ma to miejsce w przypadku Bałkanów), lecz jej obraz dotyka również mikroskali, na przykład różnicy między krajobrazem miejskim a naturalnym. Pojęcie to ma wręcz szerszy charakter, ponieważ porusza kontekst nie tylko przestrzenny, lecz również kwestię zachowań społecznych i ich ewolucję (od czasu oświecenia związaną z pojęciem postępu). Kwestia ustanowienia granicy między cywilizowanym a niecywilizowanym wciąż wpływa na kształt tożsamości współczesnych społeczeństw i dlatego warto podjąć się jej zbadania.


Author(s):  
Feng Li ◽  
Gulnigar Ablat ◽  
Siqi Zhou ◽  
Yixin Liu ◽  
Yufeng Bi ◽  
...  

AbstractIn ice and snow weather, the surface texture characteristics of asphalt pavement change, which will significantly affect the skid resistance performance of asphalt pavement. In this study, five asphalt mixture types of AC-5, AC-13, AC-16, SMA-13, SMA-16 were prepared under three conditions of the original state, ice and snow. In this paper, a 2D-wavelet transform approach is proposed to characterize the micro and macro texture of pavement. The Normalized Energy (NE) is proposed to describe the pavement texture quantitatively. Compared with the mean texture depth (MTD), NE has the advantages of full coverage, full automation and wide analytical scale. The results show that snow increases the micro-scale texture because of its fluffiness, while the formation of the ice sheets on the surface reduces the micro-scale texture. The filling effect of snow and ice reduces the macro-scale texture of the pavement surface. In a follow-up study, the 2D-wavelet transform approach can be applied to improve the intelligent driving braking system, which can provide pavement texture information for the safe braking strategy of driverless vehicles.


2006 ◽  
Vol 12 (4) ◽  
pp. 461-485 ◽  
Author(s):  
Keisuke Suzuki ◽  
Takashi Ikegami

We study a system of self-replicating loops in which interaction rules between individuals allow competition that leads to the formation of a hypercycle-like network. The main feature of the model is the multiple layers of interaction between loops, which lead to both global spatial patterns and local replication. The network of loops manifests itself as a spiral structure from which new kinds of self-replicating loops emerge at the boundaries between different species. In these regions, larger and more complex self-replicating loops live for longer periods of time, managing to self-replicate in spite of their slower replication. Of particular interest is how micro-scale interactions between replicators lead to macro-scale spatial pattern formation, and how these macro-scale patterns in turn perturb the micro-scale replication dynamics.


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