Coriolis Flowmeter Cryogenic Mass Flow Compensation
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Solution Overview
Problem
Coriolis sensors in cryogenic applications face challenges in achieving high accuracy for mass flow measurement due to non-linear changes in Modulus of Elasticity and thermal expansion, which traditional temperature correction methods fail to address effectively, resulting in inaccuracies of up to 1%.
Innovation Solution
A method that calculates compensated mass flow rate using a function independent of the Modulus of Elasticity, utilizing known fluid density and thermal expansion coefficients, as expressed in the equation ṁ = FCF ⋅ Δt − zero ⋅ ρf ⋅ 1 + α ⋅ ΔT³ + C2 ⋅ K² ⋅ C1, where ρf is calculated from an equation of state including pressure and temperature terms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional temperature correction methods are used, then the measurement process is simple, but the mass flow measurement accuracy deteriorates to 1% at best in cryogenic applications
Solution Approach 1:
The patent changes the approach from using polynomial corrections of the raw Coriolis signal to using physical parameters (thermal expansion coefficient α, density ρ, drive frequency f) to calculate a correction factor. This transforms the problem from empirical curve-fitting to physics-based calculation, improving accuracy to 0.5% while maintaining practical complexity
Solution Approach 2:
The patent introduces a correction factor CF as an intermediary element that bridges the raw Coriolis measurement and the true mass flow. This CF is calculated from thermal expansion, density, and frequency measurements, serving as a mediator that accounts for temperature effects without requiring complex direct measurements of modulus of elasticity
2Measurement precision
If polynomial temperature correction is applied, then temperature effects are compensated, but the accuracy is limited by non-linear Modulus of Elasticity changes that polynomials cannot fully capture
Solution Approach 1:
The patent replaces polynomial parameters with fundamental physical parameters (thermal expansion coefficient, density, drive frequency) that have known relationships with temperature. This change makes the correction method more reliable across varying temperature conditions, especially in cryogenic applications where polynomial fits may not generalize well
Solution Approach 2:
The patent separates the temperature compensation problem into distinct physical mechanisms: thermal expansion of the tube (affecting geometry), density changes of the fluid (affecting mass), and frequency shifts (affecting measurement). By addressing each mechanism separately with appropriate physical models, the overall reliability is improved
3Measurement precision
If the Modulus of Elasticity is measured to improve accuracy, then temperature compensation can be enhanced, but the device complexity and measurement difficulty increase significantly
Solution Approach 1:
The patent extracts the essential temperature dependence from the complex Modulus of Elasticity measurement by focusing only on the thermal expansion component. This extraction allows accurate compensation using easily measurable parameters (dimensions, density, frequency) without requiring difficult direct measurements of the Modulus of Elasticity itself
Solution Approach 2:
The patent replaces the mechanical measurement of Modulus of Elasticity (which would require complex stress-strain measurements) with a substitution based on thermal expansion theory and easily measurable geometric changes. This substitution uses the relationship between thermal expansion, frequency, and mass flow to achieve the same compensation goal without the measurement difficulty
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 achieves an accuracy of ±0.5% for mass flow measurement in cryogenic conditions, reducing the dependency on temperature measurements and minimizing uncertainties related to Modulus of Elasticity changes, thereby improving the accuracy and reliability of Coriolis sensors in cryogenic applications.
Implementation Method 1
a flowmeter sensor comprising a flow conduit to be vibrated at a drive frequency
Implementation Method 2
determining a compensated mass flow value... wherein the compensated mass flow rate is calculated as: ṁ = FCF·Δt − zero·ρf·1 + α·ΔT³ + C2·K²·C1
Implementation Method 3
The second mechanism influencing tube stiffness is the dilatation of the material with changes in temperature. If the tube is unconstrained, its length, cross section and the internal volume all change, effectively changing the stiffness.
Data Source
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AI summary
A method for determining a mass flow measurement is provided. The method comprises calibrating a flowmeter sensor at a first temperature and flowing a fluid having a second temperature through the flowmeter sensor. A density of the fluid is input into meter electronics. A compensated mass flow value of the fluid is determined by meter electronics, wherein the Modulus of Elasticity of the flowmeter sensor is unknown.