Papers by Keyword: Flow Uniformity

Abstract: Coat-hanger dies are widely used in the extrusion of polymer sheets and films. However, when designing the flat film/sheet extrusion dies manufacturing companies still facing difficulties in achieving the flow uniformity of the polymer melt. This affects the product quality and tool life. This study examines the existing extrusion die design which is used in in the industry in Kazakhstan for polypropylene sheet production and proposes better geometry of a die. These die geometries will be tested for flow uniformity in terms of velocity and pressure at the outlet.

Abstract: Various diffuser types characterized by the geometry are introduced in the flow line to recover the energy. A 3-D turning diffuser is a type of diffuser that its cross-section diffuses in all 3 directions of axes, i.e. x, y and z. In terms of applicability, a 3-D turning diffuser offers compactness and more outlet-inlet configurations over a 2-D turning diffuser. However, the flow within a 3-D turning diffuser is expected to be more complex which susceptible to excessive losses. As yet there is no established guideline that can be referred to choose a 3-D turning diffuser with an optimum performance. This paper aims to investigate the effects of varying inflow Reynolds number (Re_in) on the performance of 3-D turning diffuser with 90^o angle of turn. The outlet pressure recovery (C_p) and flow uniformity (σ_u) of 3-D turning diffuser with an area ratio (AR = 2.16) and outlet-inlet configurations (W₂/W₁ = 1.44, X₂/X₁ = 1.5), operated at inflow Reynolds number of Re_in = 5.786E+04 - 1.775E+05 have been experimentally tested. The experimental rig was developed by incorporating several features of low subsonic wind tunnel. This was mainly to produce a perfect fully developed and uniform flow entering diffuser. Particle image velocimetry (PIV) was used to examine the flow quality, and a digital manometer was used to measure the average static pressure of the inlet and outlet of turning diffuser. There is a promising improvement in terms of flow uniformity when a 3-D turning diffuser is used instead of a 2-D turning diffuser with the same AR. An unexpected trend found with a drop of pressure recovery at maximum operating condition of Re_in = 1.775E+05 shall require further investigations. The results obtained from this study will be in future used to validate the numerical codes. Upon successful validation, several other configurations will be numerically tested in order to establish the guidelines in the form of mathematical models.

Abstract: Catalytic converter is an important device of automobile engine exhaust system. Based on Hydromechanics, the relational mathematical models of catalytic converter simulation are established and the parameters are calculated. Making use of CFD numerical simulation method, a simulation is set up for the internal flow field of catalytic converter original model using fluent software. From the simulation, the internal flow characteristic is understood. On the basis of this, through the optimization idea adding a guiding device in inlet cone of catalytic converter, the uniformity of velocity of flow is improved. The simulation analysis show that the flow uniformity for internal flow field can be improved observably in the structural optimization, the increasing degree of pressure loss is with little range. A new idea and reference may be offered for improving flow uniformity of a catalytic converter.

Abstract: A turning diffuser is often introduced in the flow line to recover the energy losses by converting the kinetic energy to pressure energy. There are two types of turning diffusers, i.e. a 2-D and 3-D diffuser that are commonly defined by their expansion direction. This study aims to investigate the performance of a 2-D and a 3-D turning diffuser with 90^o angle of turn and an area ratio, AR=2.16 by means of varying operating conditions. The geometry configurations applied for a 2-D turning diffuser are outlet-inlet configurations, W₂/W_12-D=2.160, X₂/X_12-D =1.000 and an inner wall length to an inlet throat width ratio, L_in/W_12-D=4.370, whereas for a 3-D turning diffuser, they are W₂/W_13-D=1.440, X₂/X_13-D =1.500 and L_in/W_13-D=3.970. The operating conditions represented by inflow Reynolds numbers, Re_in are varied from 5.786E+04 to 1.775E+05. Particle image velocimetry (PIV) is used to examine the flow quality, and a digital manometer provides the average static pressure at the inlet and outlet of the turning diffuser. A compromise between the maximum permissible pressure recovery and flow uniformity is determined based upon the need. Whenever the flow uniformity being the need it is promising to apply a 3-D turning diffuser for Re_in=1.027E+05 - 1.775E+05 and a 2-D turning diffuser for Re_in=5.786E+04-6.382E+04. On the other hand, it is viable to opt for a 3-D turning diffuser for Re_in=5.786E+04-6.382E+04 and a 2-D turning diffuser for Re_in=1.027E+05-1.775E+05 in the case of the outlet pressure recovery being the need. The secondary flow separation takes place prior at 1/2L_in/W₁ for a 2-D turning diffuser, whereas approximately at 3/4L_in/W₁ for a 3-D turning diffuser.

Abstract: This paper presents a numerical investigation of pressure recovery and flow uniformity in turning diffusers with 90^o angle of turn by varying geometric and operating parameters. The geometric and operating parameters considered in this study are area ratio (AR= 1.6, 2.0 and 3.0) and inflow Reynolds number (Re_in=23, 2.653E+04, 7.959E+04, 1.592E+05 and 2.123E+05). Three turbulence models, i.e. the standard k-e turbulence model (std k-e), the shear stress transport model (SST-k-W) and the Reynolds stress model (RSM) were assessed in terms of their applicability to simulate the actual cases. The standard k-e turbulence model appeared as the best validated model, with the percentage of deviation to the experimental being the least recorded. Results show that the outlet pressure recovery of a turning diffuser at specified Re_in improves approximately 32% by varying the AR from 1.6 to 3.0. Whereas, by varying the Re_in from 2.653E+04 to 2.123E+05, the outlet pressure recovery at specified AR turning diffuser improves of approximately 24%. The flow uniformity is considerably distorted with the increase of AR and Re_in. Therefore, there should be a compromise between achieving the maximum pressure recovery and the maximum possible flow uniformity. The present work proposes the turning diffuser with AR=1.6 operated at Re_in=2.653E+04 as the optimum set of parameters, producing pressure recovery of C_p=0.320 and flow uniformity of su=1.62, with minimal flow separation occurring in the system.

Abstract: Injection moulding is an important manufacturing method for plastic parts. There are however many moulding quality defects caused by inappropriate setting of moulding process conditions, as well as the poorly designed plastic part geometry. Often, stiffeners are used in a plastic part to increase its strength. However, if the stiffeners are not designed properly, they will introduce one or more moulding quality problems, which in turn will worsen the part strength rather than increasing it. Although there have been quite a lot of researches on optimising moulding quality, it is often difficult to minimize multiple quality defects simultaneously. In this paper, we propose to employ flow uniformity as the optimisation objective to address this problem. A number of stiffener layout designs are evaluated in terms of this objective to determine the best design, where standard deviations of filling times and pressures at the extremities of the plastic part are used to measure the uniformity of flow. A simple case study is also presented to demonstrate the applicability of the proposed methodology.