Loop-Shaped Thermal Flow Sensor for Chromatography
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Solution Overview
Problem
Existing flow sensors for low-flow rate measurements in chromatography are susceptible to ambient temperature fluctuations and require calibration for different solvents, leading to inaccuracies and increased complexity.
Innovation Solution
A flow sensor design with a loop-shaped tube and point-source heaters and sensors, where the tube ends are thermally equilibrated to mitigate ambient temperature effects and eliminate the need for solvent-specific calibration, using a common heat sink and small, high-sensitivity thermistors for improved sensitivity and reduced noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional flow sensors with separate upstream and downstream temperature sensing are used, then flow rate measurement is enabled, but ambient temperature fluctuations cause temperature offsets between elements leading to measurement inaccuracies
Solution Approach 1:
The patent combines the upstream and downstream temperature sensing functions into a single temperature sensor located at the looped tube end. This merging eliminates the temperature offset problem between separate upstream and downstream elements caused by ambient temperature fluctuations, as both measurement references now share the same thermal environment at the tube end.
Solution Approach 2:
The patent introduces a spatial dimension change by looping the tube back on itself, bringing the downstream end to the same physical location as the upstream end. This dimensional reconfiguration allows a single temperature sensor to reference both upstream and downstream temperatures at the same spatial position, eliminating ambient temperature gradients between separate locations.
2Measurement precision
If flow sensors are calibrated for different solvents, then measurement accuracy for specific liquids is improved, but device complexity and calibration requirements increase
Solution Approach 1:
The patent creates a universal flow sensor design that can accurately measure flow rates of different liquids without requiring solvent-specific calibration. The looped tube configuration with a single temperature sensor provides a reference temperature that is independent of the liquid being measured, allowing the same sensor to universally measure flow rates across multiple liquid types.
Solution Approach 2:
The patent extracts the temperature reference function from the liquid flow path and places it at the looped tube end where it is isolated from the liquid's thermal properties. By taking out the temperature sensing reference from direct exposure to different solvents, the sensor eliminates the need for solvent-specific calibration while maintaining measurement accuracy.
3Productivity
If point-source heaters and small thermistors are used, then sensitivity and response time are improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent employs small thermistors that serve dual functions as both heaters and temperature sensors. This self-service approach eliminates the need for separate heater and sensor elements, reducing the number of components that require precise positioning and manufacturing tolerances while maintaining high sensitivity and fast response times.
Solution Approach 2:
The patent merges the heater and temperature sensor functions into a single dual-function thermistor element. This combination reduces manufacturing complexity by eliminating the need for precise alignment between separate heater coils and temperature sensors, while the small size of the thermistor maintains high sensitivity and fast response characteristics.
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 accurate flow rate measurements down to 1 nl/min with a response time of 5 seconds or less, reduces the need for temperature-controlled chambers, and eliminates the need for solvent-specific calibration, resulting in a more cost-effective and sensitive flow sensor.
Implementation Method 1
The elements 120, 130 introduce heat to a fluid in the tube 110 when a current is passed through the coils
Implementation Method 2
their temperature is measured by monitoring the resistance of the coils, which changes with a change in temperature
Implementation Method 3
providing a common ambient environment at upstream and downstream locations of a tube... positioning the ends of a tube adjacent to one another
Data Source
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AI summary
A flow sensor includes a fluidic component, such as a tube, a heat source, an upstream temperature sensor, and a downstream temperature sensors. The fluidic component defines a flow path having inlet and outlet ends disposed closer to each other than to a mid-point of the flow path. The heat source and the upstream and downstream temperature sensors are disposed in thermal communication with a fluid in the flow path.