Unterschiede
Hier werden die Unterschiede zwischen zwei Versionen angezeigt.
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| en:berechnungen:schlepp-druckstroemung [2024/10/30 13:18] – neelest | en:berechnungen:schlepp-druckstroemung [2026/09/17 16:04] (aktuell) – gelöscht - Externe Bearbeitung (Unbekanntes Datum) 127.0.0.1 | ||
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| - | ======Drag pressure flow ====== | ||
| - | The dimensionless throughput $π_{\dot m}$ describes the mass flow related to the mass flow | ||
| - | caused by the drag flow. The mass flow of the pure drag flow can be described as | ||
| - | follows: | ||
| - | |||
| - | $\dot m = 0,5 \cdot ρ \cdot h \cdot B \cdot v_0$ | ||
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| - | If the total mass flow is now related to the drag flow, this results: | ||
| - | |||
| - | $π_{\dot m} = \frac{\dot m}{(0,5 \cdot ρ(T) \cdot h \cdot b \cdot v_{0z}}$ | ||
| - | |||
| - | The dimensionless pressure gradient describes the influence of the pressure | ||
| - | gradients on the total flow. It is defined by the following equation: | ||
| - | |||
| - | $π_p = \frac{(h^{1+n} \cdot Δp)}{(6 \cdot v_{0z}^n \cdot Z \cdot n^{0,94} \cdot K(T))}$ | ||
| - | |||
| - | The two dimensionless key figures mentioned above can be used to deduce the flow | ||
| - | field in the screw. $π_{\dot m} = 1$ describes a flow that consists purely of a drag flow. There is | ||
| - | no pressure gradient here which opposes this flow. $π_{\dot m} = 0$ on the other hand means | ||
| - | that no material is conveyed. Here, the effective pressure is so high that the drag flow | ||
| - | cannot move against it. If $π_{\dot m} > 1$, the pressure flow supports the drag flow. This is | ||
| - | the case with negative pressure gradients, as is often the case in grooved barrel extruders, for example. $π_{\dot m}$ usually moves between 0 and 1. The closer $π_{\dot m}$ is to 0, | ||
| - | the better the mixing effect due to the pressure profile overlapping each other, but t | ||
| - | worse the conveying effect. | ||
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| - | The following graph shows various characteristic flow profiles for different drag and | ||
| - | pressure flows for the Newtonian case. | ||
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| - | {{ : | ||
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| - | With structure-viscous materials, the curve deviates further and further with | ||
| - | decreasing power-law coefficients (see following graphic). This is taken into account | ||
| - | in the calculation. | ||
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| - | {{ : | ||
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| - | **Symbols**: | ||
| - | |||
| - | $π_{\dot m}$ : Dimensionless mass flow | ||
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| - | $π_p$ : Dimensionless pressure gradient | ||
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| - | $ρ(T)$ : Melt density at the respective temperature T | ||
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| - | $h$ : Channel depth | ||
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| - | $b$ : Channel width | ||
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| - | $v_{0z}$ : Peripheral speed in channel direction | ||
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| - | $\dot m$ : Throughput | ||
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| - | $Δp$ : Pressure gradient | ||
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| - | $Z$ : Unwound channel length | ||
| - | |||
| - | $n$ : Power law exponent | ||
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| - | $K(T)$ : Consistency factor at respective temperature T | ||
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| - | ===Further topics=== | ||
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