Difference between revisions of "Team:BostonU HW/Model"

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After running fluid through your mixer, pictures need to be taken at the regions prior to entering the primitive and after it exits the primitive. In order to obtain RGB data from these images, image processing software such as ImageJ need to be implemented. Using ImageJ a 1 pixel wide box is created that spans the length of the channel.  The two important pieces of data that need to be obtained using this box are the average RGB value over that area, and the RGB value at the outer edge of the channel. After collecting this data we can move on to calculate the mixing efficiency.
 
After running fluid through your mixer, pictures need to be taken at the regions prior to entering the primitive and after it exits the primitive. In order to obtain RGB data from these images, image processing software such as ImageJ need to be implemented. Using ImageJ a 1 pixel wide box is created that spans the length of the channel.  The two important pieces of data that need to be obtained using this box are the average RGB value over that area, and the RGB value at the outer edge of the channel. After collecting this data we can move on to calculate the mixing efficiency.
 
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Revision as of 04:46, 30 October 2017

BostonU_HW

Videos

Evaluate your Chip with Fluid Functionality Checklist

Summary

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Picture

Quantitative

Leak (Initial)

This qualitative failure is characterized by liquid leaking out of a channel and/or primitive into the space between the PDMS and flow layer. An initial leak occurs almost immediately after a liquid passes the area of the leak. Regardless of scale, these leaks are considered a failure mode.

Leak (Over Time)

This qualitative failure is characterized by liquid leaking out of a channel and/or primitive into the space between the PDMS and flow layer. A leak that occurs over time is not characterized by an initial leak growing over time but as a leak that appears a significant amount of time after liquid has passed the location of a leak. These leaks can be seen in situations where a seal degrades during incubation period, leading to a new leak forming minutes after liquid initially passed through a section. Regardless of scale, these leaks are considered a failure mode.

Air Bubble

This qualitative failure is characterized by an air bubble being present within a channel or primitive. Air bubbles can affect proper liquid flow and can reduce the accuracy of design features such as time-dependent mixers and metering. Regardless of scale, air bubbles are considered a failure mode.

Liquid does not cross an OPEN Valve

This qualitative failure is characterized by liquid not crossing over a valve that has been opened by actuating the corresponding syringe on the control layer. This failure can exist in many forms, such as liquid pausing after filling the first portion of the valve and never crossing into the second section or leakage around the first portion of a valve. This failure is often accompanied by leakage due to pressure buildup.

Liquid crosses a CLOSED Valve

This qualitative failure is characterized by a liquid crossing over a valve that is closed, meaning that it’s corresponding control syringe has not been actuated. This failure can exist in many forms, such as liquid leaking over a valve that has never been opened before or leaking over a valve that was previously opened by is not closed. This failure can lead to contamination of liquids as well as inaccuracies with features such as metering.

Mixer does not mix liquids sufficiently

This qualitative failure is characterized by the final output of a mixer not being sufficiently mixed. This failure can be dependent on the chip being tested, as certain procedures will have varying levels of tolerance regarding mixture homogeneity. In general, liquids exiting a mixer should be relatively homogenous; a quantitative calculation of mixing can be performed to calculate how homogeneous the final mixture is.

Qualitative

PSI Calculation

When a chip's internal pressure exceeds the maximum pressure that the sealing can withstand many complications such as leaks will ensue. In order to evaluate whether the chip will be able to function without these issues a PSI calculation is needed to be performed. This quantitative test is utilized to measure the internal pressure of a specific primitive inside your microfluidic chip. The MARS chips have all been manufactured using Makerfluidics, and have been evaluated to withstand an internal pressure of up to 5 PSI. To calculate the pressure in a given primitive the following three equations need to be used.
  1. \[10h < w\] or \[2h>w\]

  2. \[12\mu L/wh^{3} < R_{fluid} < 32\mu L/wh^{3}\]

  3. \[\Delta P=R_{fluid}Q\]
Equations a-c are used to describe the relationship of pressure within a channel of a given length, width, and height. Equation a is used to determine which formula in equation b will provide a better approximation of fluid resistance based on the primitive dimensions. After determining an approximate value of fluid resistance, PSI can be calculated using equation c. Equation c is analogous to Ohm’s law but is used for fluid dynamics. The PSI value is directly proportional to both the fluid resistance and the flow rate. These calculations were written as a C++ file which can be compiled and executed.

Mixer Effiency

The mixing of two fluids is something that can often be qualitatively observed, however in order to properly perform an experiment certain amounts of mixing must be achieved. In order to evaluate the degree of which fluids are being mixed in a mixer primitive a mixer efficiency test is needed to be performed. This quantitative test is broken down into a two part process:
  1. Image Processing
    2. After running fluid through your mixer, pictures need to be taken at the regions prior to entering the primitive and after it exits the primitive. In order to obtain RGB data from these images, image processing software such as ImageJ need to be implemented. Using ImageJ a 1 pixel wide box is created that spans the length of the channel. The two important pieces of data that need to be obtained using this box are the average RGB value over that area, and the RGB value at the outer edge of the channel. After collecting this data we can move on to calculate the mixing efficiency.
  2. Efficiency Calculation The efficiency of the mixing itself can be measured using the following equation. Once this value is obtained the channel primitive is able to measured to see if it is suitable to perform the needed function.