Flow paths, complex geometry

Some tests are affected by core orientation and some test properties are more influenced by surface orientation. Since orientation is not uniform, but has a gradient through and along the flow path, it is difficult to predict directly the effects of process conditions on part properties, without a complex model of the part geometry and estimation of flow characteristics in the cavity. 

When the mold contains more than one identical mold cavity, it is important that the cavities fill equally. The usual approach to accomplishing this is to balance the flow paths for the plastic, so that distances and geometry, and thus pressure and flow, are equalized. Where nonidentical objects are being produced, this job is even more complex, but that seldom applies in packaging applications. It is also important to design the runner geometry to avoid dead spots, where plastic can accumulate and be subjected to an excessive heat history. 

Complex geometry of pr erential flow paths (as afifected by rock discontinuity and heterogeneity on all scales—from a rough fracture surfece to an irregular fracture network). 

The complex geometry of flow padis in fractured rock results, primarily, fivm rock discontinuities that are present on aU scales, extending from the microscale of microfissures (ammig the mineral components of the rock) to the macroscale of various types of joints and fruits (29, 30). The complexity of the fracture-network geometry can cause either divergence or convergence of localized and nonuniform flow paths in different parts of fractured media, as well as cq>illary barrier effects at the intersection of flow paths. 

Laboratory and field experiments show die presence and interplay of such processes as intrafracture film flow along fracture surfaces, coalescence and divergence of multiple flow paths along fracture surteces, and intrafracture water dripping. The nonlinear dynamics of flow and transport processes in unsaturated fractured porous media arise from die dynamic feedback and conpetition between various nonlinear physical processes along widi the complex geometry of flow paths. The apparent randomness of (he flow field does not prohibit the system s determinism and is, in fact, described by deterministic chaotic models using deterministic differential or difference-differential equations. 

Amorphous materials sinter by viscous flow and crystalline materials sinter by diffusion, so the paths along which material moves, and the relationship between the rate of transport and the driving force, are quite different [21. Analysis of viscous sintering is relatively simple in principle, but exact treatments are prevented by the complex geometry of the porous body. Fortunately, simple approximations, while not strictly realistic, yield satisfactory results. ... 

The flow direction is shown to be in the clockwise sense, but NCLs will operate in either direction, unless means are employed to ensure unidirectional flow. In addition, the very simple geometry of the loop shown in Fig. 16.3 is an idealization of the possible geometry of NCLs, which instead may be complex, having different path lengths, flow areas, and plumbing fixtures. 

Injection pressure also adds heat to the material on its way to the mold in the form of shear or frictional heating. Excessive injection pressure can cause local burning in material or overall degradation. Pressure requirements are also a function of part and tool geometry. Large part volumes, thin walls, tortuous flow paths, and geometric complexity can add to the difficulty of delivering melt to the mold in an acceptable time frame. 

As velocity of flow increases, a condition is eventually reached at which rectilinear laminar flow is no longer stable, and a transition occurs to an alternate mode of motion that always involves complex particle paths. This motion may be of a multidimensional secondary laminar form, or it may be a chaotic eddy motion called turbulence. The nature of the motion is governed by both the rheological nature of the fluid and the geometry of the flow boundaries. 

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