Capacitive Pipe Electrodes for Durable Electromagnetic Velocity Tomography
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Solution Overview
Problem
Existing electromagnetic velocity tomography (EVT) apparatus for monitoring fluid flow in pipes face issues such as electrode erosion, corrosion, electrochemical effects, and structural integrity due to direct contact with the fluid, which limits their accuracy and reliability, especially in multiphase flows.
Innovation Solution
The apparatus employs capacitively-coupled non-contacting electrodes integrated into a flexible printed circuit board around the pipe, generating magnetic fields and detecting flow-induced voltages without direct physical or electrical contact, using a cosine coil configuration and signal processing circuitry to enhance accuracy and durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If electrodes are exposed at the inner surface of the pipe and in direct contact with the fluid, then flow induced voltages can be detected, but the electrode surface becomes eroded, worn, corroded, damaged or soiled during use
Solution Approach 1:
A dielectric coating is applied to the electrode surface, serving as an intermediary layer that electrically isolates the electrode from direct contact with the fluid while still allowing capacitive coupling to detect flow-induced voltages. This resolves the contradiction by enabling voltage detection through the dielectric barrier without the electrode suffering from erosion, corrosion, or fouling that would occur with direct fluid contact.
2Measurement precision
If electrodes are exposed at the inner surface of the pipe, then flow induced voltages can be detected, but a large direct current offset voltage is generated as a result of electrochemical interactions
Solution Approach 1:
The dielectric coating acts as an intermediary that blocks electrochemical interactions between the electrode and the conductive fluid. By preventing direct electrical contact, the dielectric layer eliminates the generation of large direct current offset voltages that result from electrochemical reactions, while still permitting the detection of alternating flow-induced voltages through capacitive coupling.
3Strength
If electrodes are embedded in the pipe wall, then structural integrity is maintained, but electrical connectors need to extend through holes drilled through the pipe wall which may compromise structural integrity
Solution Approach 1:
The dielectric coating serves as an intermediary that enables electrical isolation without requiring physical penetration of the pipe wall. By allowing capacitive coupling through the coating, the system eliminates the need to drill holes through the pipe wall for electrical connectors, thereby maintaining the structural integrity and strength of the pipe wall while still enabling electrical connection for signal detection.
4Reliability
If non-contacting capacitively-coupled electrodes are used, then electrode durability is improved, but signal strength is reduced compared to direct contact electrodes
Solution Approach 1:
The system compensates for the reduced signal strength from capacitive coupling by optimizing parameters such as the dielectric thickness, dielectric material properties (permittivity), electrode surface area, and signal amplification gain. By adjusting these parameters, the system maintains sufficient signal strength for accurate flow measurement while retaining the durability advantages of non-contacting electrodes.
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
This design provides highly accurate, real-time monitoring of fluid flow velocity profiles with improved signal strength, reduced maintenance, and enhanced structural integrity, suitable for multiphase flows in the oil and gas industry.
Implementation Method 1
A coil system comprising electrically conductive wires is located externally of the flow conduit for generating composite magnetic fields within the flow conduit. A magnetic signal driving circuitry is electrically connected to the coil system, and is arranged to pass electrical current through the coil system thereby to transmit a magnetic field from the coil system into the flow conduit.
Implementation Method 2
when electrically conducting fluid, such as an aqueous phase, flowing along the pipe passes through the magnetic field, flow induced voltages are generated by magnetic induction which are detected by electrodes
Implementation Method 3
it has been proposed to provide non-contacting electrodes which do not contact the flowing fluid and which are capacitively-coupled to the fluid in order to detect flow induced voltages in the fluid flow
Data Source
AI summary
Apparatus for monitoring fluid flow in a pipe using electromagnetic velocity tomography An apparatus for monitoring a fluid flow in a pipe using electromagnetic velocity tomography (EVT), the apparatus comprising a pipe defining a flow conduit, a coil system comprising electrically conductive wires located externally of the flow conduit for generating composite magnetic fields within the flow conduit, a magnetic signal driving circuitry electrically connected to the coil system which is arranged to pass electrical current through the coil system thereby to transmit a magnetic field from the coil system into the flow conduit, a plurality of measurement electrodes located around the flow conduit for detecting voltages induced in an electrically conducting fluid flowing thorough the magnetic field, and a signal processing circuitry electrically connected to the plurality of measurement electrodes for receiving flow induced voltage signals from the electrodes, wherein the plurality of measurement electrodes is comprised in a flexible printed circuit board which is positioned circumferentially around the pipe, the printed circuit board comprising a first lamina, the first lamina comprising an electrically conductive layer which is patterned to form an annular serial array of mutually spaced measurement electrodes around the pipe which are separated from the flow conduit by at least a portion of a thickness of the pipe, wherein the pipe is comprised of an electrically non-conductive material whereby when, in use, an electrically conductive fluid is present in the flow conduit, each measurement electrode and a respective areal portion of the pipe thereunder, form, together with the electrically conductive fluid, a respective sensor which is capacitively coupled to a portion of the electrically conductive fluid in the fluid conduit.