D E N T O N L A B

R . E . U . S U M M E R 2 0 1 4

•●◊●•

E L I Z A D A W S O N

Airflow Optimization in

Real Time Atmospheric Pressure

Mass Spectrometer

Introduction

Eliza Dawson

Mechanical Engineering

The Denton Lab

Bonner Denton, Roger Sperline, Tyler Fenimore

Explosive Detection Technology: Real Time Atmospheric Pressure Mass Spectrometry

Summer Research

Airflow optimization using computer modeling and simulation

Applications of Real Time Atmospheric Pressure Mass Spectrometry

Airport Security

Vehicle Checkpoints

Public Transportation

IED detection

The above diagram illustrates how different species move across the drift region at different rates toward the detector plates.

Low Resolution Power occurs when the peak current of a particular species reaches the detector over a relatively longer period of time.

High Resolution Power occurs when a particular species moves across the drift region at a uniform rate.

Spectral Resolution

Red: 18.8 Blue: 14.1 Green: 9.1

Spectral Resolution

Resolution Power =

𝑓𝑙𝑖𝑔ℎ𝑡 𝑡𝑖𝑚𝑒 (𝑚𝑠)

𝑝𝑒𝑎𝑘 𝑤𝑖𝑑𝑡ℎ (𝑚𝑠)

If the spectral resolution drops too low, it becomes impossible to differentiate between species.

Variables that Reduce Spectral Resolution

Uneven heat distribution

Drift region turbulence and airflow

Other Considerations:

• Atmospheric Pressure

• Diffusion

• Electric field strength (voltage gradient)

Reduction of Turbulent Intensity in the Drift Region

The Challenge:

Reduce the airflow and turbulent intensity within the drift region.

Airflow through the Ionizing Region is fast moving.

Reduce airflow/turbulence in the Drift Region WITHOUT having negative effect on heat distribution.

Possible Solutions

Louvers

Baffles

Airfoils

More louvers…

Bigger airfoils?

V1.0 V2.0

Results

Average Turbulent Intensity: 21.2%

Average Velocity: 0.045 m/s

Average Turbulent Intensity: 23.4%

Average Velocity: 0.039 m/s

Results

Versions 1.1 and 2.1 included an airfoil near the trailing edge and a louver assembly at the inlet.

V1.1

Results

V2.1

Average Turbulent Intensity: 23.7%

Average Velocity: 0.037 m/s

Average Turbulent Intensity: 21.8%

Average Velocity: 0.040 m/s

Results

Versions 1.2 and 2.2 included an airfoil near the trailing edge at 10° and a louver assembly at the inlet.

V1.2 V2.2

Results

Average Turbulent Intensity: 18.5%

Average Velocity: 0.044 m/s

Average Turbulent Intensity: 17.5%

Average Velocity: 0.044 m/s

Results

Versions 1.3 and 2.3 included a modified louver assembly at the inlet and every other drift ring has been removed.

V1.3 V2.3

Average Turbulent Intensity: 14.7%

Average Velocity: 0.061 m/s

Average Turbulent Intensity: 15.2%

Average Velocity: 0.050 m/s

*Note that the turbulence does decrease, but the airspeed and quantity also increases.

Considerations in Interpreting these Results

Velocity and Turbulent Intensity

𝑇𝑢𝑟𝑏𝑢𝑙𝑒𝑛𝑡 𝐼𝑛𝑡𝑒𝑛𝑠𝑖𝑡𝑦 =𝑆𝑡𝑎𝑛𝑑𝑎𝑟𝑑 𝑑𝑒𝑣𝑖𝑎𝑡𝑖𝑜𝑛 𝑜𝑓 𝑡ℎ𝑒 𝑚𝑒𝑎𝑛 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦

𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦

Works well at high velocities, but not at low velocities

Air velocity in the drift region

Average airspeed in the drift region is SLOW by comparison to ion drift velocity.

Conclusions

What we know now

Exchange between the ionizing region and the drift region is inevitable due to pressure differences.

Turbulence and velocity are already close to optimized.

A better way to reduce the effect of airflow in the drift region may be to increase the electric field strength.

Acknowledgements

Questions?

Thank you to The National Science Foundation Denton Lab

Bonner Denton Roger Sperline Jeff Babis Rob Kingston Justin Keogh Mary Kay Wray

REU mentors and peers Dr. Srin Manne Rebekah Cross Nikita Kirnosov Amanda Halawani