Crossed-Spring Pivot Rheometer with Force Rebalance
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Solution Overview
Problem
Conventional apparatuses for measuring fluid rheology, especially in harsh environments, fail to accurately measure viscoelastic properties of non-Newtonian fluids due to limitations in bearing reliability and inability to handle extreme conditions such as high temperatures and pressures.
Innovation Solution
The use of a force rebalance system in conjunction with a crossed-spring pivot rheometer that allows for controlled rotational displacement and oscillatory measurements, enabling accurate determination of shear stress, shear modulus, and other viscoelastic properties by counteracting torque with an electromagnetically generated opposing force and using digital signal processing for precise parameter extraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional ball or roller bearings are used to suspend the bob and sleeve, then the apparatus can operate in harsh environments, but the bearings become pitted or gummed up resulting in inaccurate viscosity measurements and instrument failure
Solution Approach 1:
The patent replaces conventional ball or roller bearings with a flexural pivot bearing system. The flexural pivot uses elastic deformation of a support structure to enable rotation without sliding or rolling friction, eliminating the mechanical contact that causes pitting and gumming in traditional bearings. This substitution maintains reliability in harsh environments while preserving measurement accuracy.
Solution Approach 2:
The patent changes the fundamental operating parameters of the bearing system by transitioning from high-friction sliding/rolling contact to low-friction flexural deformation. The flexural pivot operates through elastic bending rather than mechanical contact, fundamentally altering the friction and wear characteristics to prevent bearing failure in high-temperature and high-pressure drilling environments.
2Measurement precision
If a cross-spring pivot is used as the flexural bearing, then rotational properties become very consistent with no sliding or rolling friction, but the device lacks the ability to measure viscoelastic fluid properties such as the shear modulus
Solution Approach 1:
The patent enhances the cross-spring pivot rheometer to perform multiple measurement functions. By incorporating oscillatory motion capability alongside the existing rotational measurement function, the device can now measure both Newtonian viscosity and viscoelastic properties such as shear modulus. This multi-functionality is achieved while maintaining the consistent rotational properties provided by the flexural pivot bearing.
Solution Approach 2:
The patent introduces dynamic oscillatory motion to the rheometer system. The ability to oscillate the bob or sleeve allows the device to probe viscoelastic properties through time-dependent measurements. This dynamic capability complements the static rotational measurement function, enabling comprehensive rheological characterization of both Newtonian and non-Newtonian fluids.
3Measurement precision
If the sleeve is rotated at a known velocity to measure viscosity, then the torque exerted on the bob provides a measure of fluid viscosity, but the apparatus cannot perform oscillatory rheology measurements or constant shear rate measurements
Solution Approach 1:
The patent transforms the rheometer from a static rotational measurement system to a dynamic system capable of multiple motion modes. The control system can now implement oscillatory rotation of the sleeve or bob in addition to constant velocity rotation, enabling oscillatory rheology measurements. This dynamic capability allows the apparatus to perform constant shear rate measurements and viscoelastic property measurements while maintaining accurate viscosity measurement through torque detection.
Solution Approach 2:
The patent incorporates feedback control mechanisms to maintain precise control over the rotational velocity and oscillation parameters. The torque sensor provides real-time feedback about the fluid resistance, allowing the control system to adjust the driving mechanism to maintain constant shear rate or constant oscillation amplitude. This feedback ensures measurement accuracy across different rheology measurement types.
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 approach enhances the reliability and accuracy of rheological measurements, allowing for the characterization of both Newtonian and non-Newtonian fluids under extreme conditions, providing precise data on shear stress, viscoelastic properties, and gel properties, including the breaking point and peak shear stress.
Implementation Method 1
A typical CSP is an arrangement of several flat springs configured so that when rotated for small angles, the springs bend so that the deflection appears to be about an axis
Implementation Method 2
The CSP acting as a torsion spring and bearing support for the bob
Implementation Method 3
counteracting torque with an electromagnetically generated opposing force
Data Source
AI summary
A rheometer instrument including a stationary frame, a sleeve suspended from the frame, a bob suspended within the sleeve, a cross-spring pivot suspending the bob from the stationary frame, and a force rebalance system for effecting the rotational displacement of the bob with a torque. The force rebalance system includes an arm attached to the movable portion of the cross-spring pivot, a rotational position sensor in close proximity to the arm for measuring the rotational displacement and angular frequency of the arm, and a force actuator positioned to apply force to the arm. The rheometer instrument may be used to calculate the rheological properties of Newtonian and non-Newtonian fluids.