Dual Tapered Microfluidic Flow Restrictor for Bubble Management
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Solution Overview
Problem
Micro-capillary flow restrictors in medical infusion devices face unpredictable bubble fragmentation, leading to reduced flow rates or blockages, which complicates mass production and affects the reliability of medical infusion systems.
Innovation Solution
A flow restrictor design with a converging tapered inlet and a diverging tapered outlet, featuring a constant internal diameter section, is implemented to minimize bubble fragmentation and noise in sensors, by ensuring a smooth transition in channel diameter and reducing the likelihood of bubble pinning at the outlet.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional micro-capillary flow restrictors are used, then flow restriction is achieved, but bubble fragmentation occurs leading to unpredictable flow rates and blockages
Solution Approach 1:
The inlet of the micro-capillary is designed with a curved radius R instead of a sharp edge. This curvature prevents the formation of stress concentration points that would otherwise cause bubble fragmentation. The smooth curved surface allows bubbles to pass through without being pinned or fragmented, thereby improving flow rate consistency and eliminating the harmful bubble fragmentation effect.
2Reliability
If multiple flow restrictors are tested in production, then yield can be assessed, but manufacturing efficiency is reduced due to unpredictable fragmentation behavior
Solution Approach 1:
The invention changes the geometric parameter of the inlet from a sharp edge to a curved radius R. This parameter change fundamentally alters the flow dynamics and bubble behavior, making the device predictable in its performance. The curvature radius becomes a controllable parameter that ensures consistent behavior across all manufactured devices, eliminating the need for extensive testing and improving manufacturing yield.
3Ease of manufacture
If standard capillary cutting methods are used, then production is simple, but inlet contours vary leading to inconsistent bubble fragmentation behavior
Solution Approach 1:
The curved inlet radius R is incorporated into the capillary manufacturing process itself, rather than requiring post-manufacturing processing or assembly of pre-formed inlets. This preliminary action ensures that every capillary emerges from production with the correct curved inlet geometry, guaranteeing consistent bubble behavior without adding complex assembly steps or reducing manufacturing simplicity.
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 significantly reduces bubble fragmentation and noise in flow or pressure sensors, enhancing the predictability and yield of micro-capillary flow restrictors, leading to more reliable and consistent liquid flow rates in medical infusion devices.
Implementation Method 1
bubbles of gas in the liquid may have a serious impact on the pressure difference or pressure drop required to drive a given flow rate through the capillary and, in the worst case, bubbles may lead to an effective blocking of the capillary. This is due to the phenomenon of fragmentation of a larger bubble at the inlet of the capillary into a plurality of small bubbles within the capillary.
Implementation Method 2
Delivery of liquids at flow rates of up to a few milliliters per hour or less may be achieved by connecting a source of pressurized liquid to a capillary of small internal diameter. The rate of flow through the capillary has a well-defined relation to the length and internal diameter of the capillary, and to the difference in pressure between the capillary inlet and the capillary outlet.
Implementation Method 3
The rate of flow through the capillary has a well-defined relation to the length and internal diameter of the capillary, and to the difference in pressure between the capillary inlet and the capillary outlet.
Data Source
AI summary
Embodiments of the present invention relate to a microfluidic flow restrictor having a converging tapered inlet connected by a constant internal diameter section to a diverging tapered outlet having an outlet face and a smooth and gradual transition from the constant internal diameter section to the outlet face. This dual tapered capillary flow restrictor may be incorporated into a system such as a microfluidic circuit. Using a dual tapered capillary for accurate flow control together with a constant pressure source provides a more steady flow with reduced flow fluctuation caused by bubbles passing or pinning to the capillary end-face. Further, when connected in series, these dual tapered capillary flow restrictors may reduce noise in flow and pressure measurements, reduce bubble segmentation, and reduce bubble pinning.