Conductivity Flow Measurement for Dirt-Tolerant Bubble Detection
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Solution Overview
Problem
Existing flow velocity measurement methods in sewage treatment plants are hindered by dirt layers in delivery lines, making it difficult to reliably determine water flow velocity, especially with optical or photometric air bubble transit time measurements.
Innovation Solution
A conductive flow velocity measurement arrangement using two electrical conductivity cells and an air bubble injector to measure flow velocity based on conductivity changes, allowing reliable detection of air bubbles even with thick dirt layers, by calculating transit time and flow velocity from conductivity profiles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical or photometric air bubble transit time measurement is used, then flow velocity can be determined, but the useful signal deteriorates considerably as the dirt layer increases
Solution Approach 1:
The patent replaces optical measurement methods with electrical conductivity measurement. Instead of using light to detect air bubbles, the system uses conductivity measurement cells that detect changes in electrical conductivity when air bubbles pass through. This substitution eliminates the problem of optical signal deterioration caused by dirt layers, as electrical conductivity measurement is not affected by visual obstruction.
Solution Approach 2:
The patent changes the measurement parameter from optical properties to electrical conductivity. By measuring the electrical conductivity of the liquid instead of its optical properties, the system achieves immunity to dirt layer interference. The conductivity measurement remains reliable even when thick dirt layers are present on the inner walls of the measurement cells.
2Ease of repair
If peristaltic pump is used for sampling, then the fluidic part can be easily replaced, but the flow rate measurement cannot be used to determine the amount of water pumped due to elastic and plastic deformation
Solution Approach 1:
The patent introduces a separate measurement line with defined length as an intermediary between the sampling pump and the analysis unit. This measurement line serves as a reference path for conductivity-based flow velocity measurement, allowing accurate determination of water quantity independent of the pump's deformation. The measurement line provides a stable geometric reference that compensates for the pump's elastic and plastic deformation.
3Speed
If air bubble injection is used for flow velocity measurement, then transit time can be measured, but the signal quality deteriorates with increasing dirt layer thickness
Solution Approach 1:
The patent replaces optical detection of air bubbles with electrical conductivity detection. The measurement cells measure changes in electrical conductivity as air bubbles pass through, providing a reliable signal that is not degraded by dirt layers. This substitution maintains signal detection reliability while enabling flow velocity measurement in dirty environments.
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
Provides a dirt-tolerant flow velocity measurement that accurately determines flow velocity and detects blockages, even with significant dirt buildup, using a simple and cost-effective method.
Implementation Method 1
The flow velocity measurement arrangement determines the presence of one or more injected air bubbles not optically, but conductively. The first electrical conductivity measurement cell is thus arranged downstream of the air bubble injector and upstream of the measurement line, whereas the second electrical conductivity measurement cell is arranged downstream of the measurement line.
Implementation Method 2
The measurement arrangement has an air bubble injector for injecting one or more air bubbles into a water sample liquid stream.
Implementation Method 3
the evaluation unit records, for example, the time-related conductivity profile in the first conductivity measurement cell and, in the second conductivity measurement cell, compares these profiles with each other, and determines the transit time between the two conductivity measurement cells
Data Source
AI summary
A flow velocity measurement arrangement (10) for determining the flow velocity of an electrically conductive liquid in a liquid line, comprising an air bubble injector (82) for injecting an air bubble into a liquid flow, a first electrical conductivity measurement cell (30) downstream of the air bubble injector (82) and upstream of a measurement line (40), a second electrical conductivity measurement cell (30′) downstream of the measurement line (40), an evaluation unit (20) which determines the flow velocity of the liquid in the measurement line (40) on the basis of the time-related characteristics of the conductivity measurement results of the two measurement cells (30, 30′).