Inline Viscosity Measurement Device for PVC Melt Wall Slip
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Solution Overview
Problem
Conventional inline viscosity measurement devices for PVC melts face challenges in providing reliable and reproducible viscosity measurements due to the wall sliding phenomenon, which affects pressure loss measurements and leads to inaccurate viscosity determination.
Innovation Solution
An inline viscosity measurement process and device that measure pressure differences by using a measurement route with installation elements, such as stem elements, arranged in a specific configuration to minimize wall sliding effects and ensure reproducible pressure loss measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional orifice plate measurement is used, then the device complexity is low, but the measurement precision deteriorates due to wall slip effects
Solution Approach 1:
The measuring channel is divided into multiple sections with different cross-sectional areas, creating a segmented flow path that prevents wall slip by varying the flow conditions along the measurement route
Solution Approach 2:
Different sections of the measuring channel have different geometric properties (cross-sectional areas) to create specific local flow conditions that eliminate wall slip effects at critical measurement points
2Measurement precision
If measurement is performed in the thin layer near channel wall, then the device complexity is low, but the measurement precision deteriorates due to wall friction influence
Solution Approach 1:
The measurement is shifted from the wall region to the central flow region by using a measuring channel with varying cross-section, allowing pressure drop measurement to reflect bulk melt viscosity rather than wall layer properties
3Reliability
If conventional inline viscometer with bypass or melt pump is used, then the viscosity measurement can be performed, but the reliability deteriorates due to excessive residence time causing product degradation
Solution Approach 1:
The measurement is performed continuously in the main extrusion flow path without diverting the melt through bypass channels or requiring melt pumps, eliminating additional residence time and maintaining measurement reliability
Solution Approach 2:
The viscosity measurement function is merged with the main extrusion process flow, using the production channel itself as the measurement channel, so no separate measurement path is needed
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enables continuous, reliable, and inexpensive inline viscosity measurement of PVC melts, effectively addressing the limitations of conventional methods by providing accurate and reproducible viscosity data.
Implementation Method 1
measuring a pressure difference to determine the viscosity of a flowable medium
Implementation Method 2
PVC experiences what is known as wall slip. Wall slip is a rheological phenomenon that is only observed in a small number of polymers, including PVC
Data Source
Figure 1a~2b
Figure 3a~4b
Figure 5a~6b
AI summary
The invention relates to a method for measuring a pressure difference to determine the viscosity of a fluid medium, and to an associated device. The fluid medium flows through a measuring section arranged in a pipe element (1), in which at least one installation element (5) is arranged, wherein an inlet pressure at an inlet end (3) of the pipe element (1) and an outlet pressure at an outlet end (4) are measured. A differential pressure between the inlet pressure and the outlet pressure is determined by means of a computing unit (8). The installation element (5, 6) is designed as at least one web element.