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Ocena poprawki Bagleya na podstawie pomiarów w linii wytłaczarskiej

Kloziński A., Sterzyński T.

Polimery

2005

T. 50, nr 6

455-462

Pomiary poprawki Bagleya (eB) tradycyjnie realizuje się za pomocą reometrów kapilarnych, natomiast w artykule przedstawiono metodę wyznaczania wartości eB na podstawie pomiarów prowadzonych w rzeczywistych warunkach przetwórczych. Jako urządzenie pomiarowe zastosowano reologiczną głowicę z wymiennymi dyszami, zamontowaną do korpusu wytłaczarki jednoślimakowej. Badania przeprowadzono przy użyciu dwóch handlowych rodzajów polietylenów małej gęstości (PE-LD). Specyfika działania układu uplastyczniania wytłaczarki, dalece różniącego się od układu uplastyczniania reometru kapilarnego, wymusiła konieczność opracowania odpowiedniej procedury pomiarowo-obliczeniowej umożliwiającej ocenę eB w trakcie trwania procesu wytłaczania. Poprawkę Bagleya wyznaczono w zakresie szybkości ścinania 27-629 s-1. Wymienność dysz pomiarowych pozwoliła na określenie wpływu elementów geometrycznych kanału na wartość eB. Na podstawie przebiegu profili prędkości dokonano interpretacji różnic wartości poprawki Bagleya w zależności od rodzaju PE-LD i wymiarów dysz pomiarowych.

Bagley correction (eB) measurements usually are done using capillary rheometers. In this article a method of eB value determination on the basis of the measurements done in real processing conditions is presented. Extrusion head with exchangeable dies (Fig. 3, Table 2) installed to the single-screw extruder was used as a measuring device. Two commercial grades of low-density polyethylene (PE-LD) (Table 1) were used. The peculiarity of the action of plastifying system of an extruder, far different from plastifying system of capillary rheometer, forced us to elaborate the special measuring - computational procedure allowing to evaluate eB during the process of extrusion (Fig. 4-6). Bagley correction was determined for shear rate range from 27 s-1 up to 629 s-1 (Table 3). Ability of dies to be exchanged allowed estimating the effect of geometric elements of the channel on eB value (Fig. 7-9). On the basis of velocity profiles courses (Fig. 10 and 11) the interpretation of differences in Bagley correction value, dependently on PE-LD grades and measuring dies' dimensions, has been done.

Numerical modelling of fluid flow and heat transfer in microchannels

Favre-Marinet M., Gamrat G., Asendrych D.

Turbulence : international journal

2004

Vol. 10

75-75

The work concerns three-dimensional numerical modelling of fluid flow and heat transfer in large-span rectangular microchannel. Channel height being the key geometrical parameter, was varied hi the range from 0.3 to 1 mm. The width of channel was equal to 250 mm what allowed to treat microchannel as a two-dimensional. The computational domain followed the details of experimental facility used in preceding research step. The numerical model assumed the laminar flow of water (506 < Re < 2023) with temperature-independent properties. The results obtained in experimental trials exhibited strong reduction of Nusselt number in comparison to theoretical law. The motivation of current simulation was to identify the reasons of discrepancies between theoretical predictions and experimental results. Among the explanations the effect of axial conduction resulting from complex geometry was supposed to have the highest significance. Main goal of current work was numerical prediction of coupling conduction-convection effect and its influence on Nusselt number values. Additionally the influence of entrance effects on the deviation of beat transfer results from the macroscale laws was taken into consideration. Comparison between experimental and numerical results was an essential part of current work and allowed to point out the weakness of some simplifications being assumed during interpretation of experimental data (i.e. uniform distribution of heat flux along fluid/solid interface turned out to be the origin of significant errors). Furthermore numerical simulations exhibited that significant part of heat resulting from conduction and insufficient insulation was delivered to water in inlet container. It could lead to false estimation of bulk temperature at channel inlet and to reduction of heat transfer effectiveness at the beginning part of microchannel. Results of current work allowed not only for verification of experimental conclusions, but also pointed out the weakness of already utilised experimental setup and were helpful in a design of a new experimental installation.