Measurement of Air Temperature using Thermochromic Liquid Crystal Technology

Undergraduate Research Distinction Defense Presentation 2015 April 10

ZHENGDI WANG

Examination Committee:

Professor Randall Mathison (advisor) Professor Michael Dunn

The Ohio State University Department of Mechanical and Aerospace Engineering

Gas Turbine Laboratory

Presentation Overview

Introduction

Main purpose

Design and Experiments

Results

Conclusion and future Work

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What is Thermochromic Liquid Crystal Technology?

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Figure :1http://www.thermometersite.com/temperature-research-and-testing-kits/chiral-nematic-sprayable-liquid-crystal/detailed-product-flyer.html 2http://www.thermometersite.com/components/com_virtuemart/shop_image/product/aa28d3ecf3ebaa931c26dd86c791ff56.jpg 3 http://www.explainthatstuff.com/thermochromic-materials.html

• Heat Transfer or thermal measurement and mapping • Corresponding react to changes in temperature • Active range • Inexpensive • Quantitative measurements, associated with a measurable

scalar-- Hue angle

Color change due to the hand temperature

Incoming light waves reflect off nearby crystals and add together by interference, which produces the reflection. The color of the reflected light depends in a very precise way on how closely the crystals are together. Heat up or cool down liquid crystals will change the spacing between them, altering the amount of interference and changing the color of the reflected light from black, through red and all the colors of the spectrum to violet and back to black again. In a nutshell, the liquid crystals look a different color depending on what temperature they are because changes in temperature make them move closer together or further apart (depending on the material).

Typical color play of thermochromic liquid crystals(𝑇𝑟𝑒𝑑 < 𝑇𝑔𝑟𝑒𝑒𝑛 < 𝑇𝑏𝑙𝑢𝑒)

Test Facility --Blowdown Wind Tunnel

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Main Purposes

To build a TLC thermal model on filaments to measure and map the air temperature change in the test section of a blowdown wind tunnel.

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Existing Methods Thermocouple

– Advantage • Large Temperature range, -200

• Robust

• Rapid response

• No self heating

– Disadvantage • Complex signal conditioning

• Susceptibility to corrosion

• Susceptibility to noise

• Can only determine temperature at one point or a small array of points

• Boundary layer temperature is hard to be measured

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Figure: http://www.analog.com/library/analogdialogue/archives/44-10/thermocouple.pdf

Thermocouple rake with 11 thermocouples on it

Previous Experiments

– Long time to reset

– Infrared cameras • High cost

• Not work for spinning environment

The previous calibration experiment designed for heat flux measurement.

In my research I will use the similar strategy to do temperature measurement.

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Figure :INTERNAL COOLING IN TURBOMACHINERY, R. Poser & J. vonWolfersdorf

Experiment Process

Design test piece 1

Vacuum Oven Calibration 1

•Heat up the vacuum oven

•Take video during the experiment process

Computer analysis

•Build a Matlab program

•Determine RGB value and convert to HSV

•Make sure the TLCs active on the filaments and in the right trend

Redesign and build test piece 2

Vacuum Oven Calibration 2

•Build the accurate relationship between temperature and hue

Wire Reaction time

Measurement test

Temperature Measurement in the blowdown

wind tunnel

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Methodology--Calibration I

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Fishing line • 0.015m diameter • 1/8 inch apart

Unheated filament

Heated filament

Vacuum Oven

Camera right in front of the window

Test Piece 1

Use a blanket covering the oven to keep the experiment in a dark environment

Calibration I Results

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Those images were from the video recorded for calibration I. The video length was 709 seconds and there were 21000 frames stored in Matlab. Every 70th frame was processed, so there were a total 300 images used for extracting hue value. 80 points on the filaments were selected (as shown in the images) and they were the same location in all 300 images.

Calibration I Results

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• TLC did have color change on the small surfaces (0.015m diameter fishing line)

• The camera was clear enough to record the experiment

• A clear relationship between the color change and temperature rise has been demonstrated.

Methodology-Calibration II

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Methodology-Calibration II

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LEDs—Light source

Camera

Calibration wires

RTD Sensor

Wires

Calibration II Results

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Cool down process--starts from 93℉(33.5℃)

Calibration II Results

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-

• Timothy Lawler processed the data from the oven calibration. • Third order polynomial curve fit ( 95% confidence bounds) • 𝑇𝑒𝑚𝑝 𝐾 =(-2.413× 10−6)(𝐻𝑢𝑒)3+0.001961(𝐻𝑢𝑒)2−0.1785𝐻𝑢𝑒 + 304.5

Comparison of data fit within the range of interest

Tem

per

atu

re [

k]

Hue

Fit Real Data

60 100

Methodology-Reaction Time Measurement

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Camera

Test piece 2

LEDs--Light Sources

Fishing line • 0.015m diameter

Heat Source

Top view

Side View

Reaction Time Measurement

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Reaction Time Measurement Results

• Select 4 points on the color changing region on wires

• Frame rate of the video is 30 frames per second

• Process each run in Matlab to determine the reaction time

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Points Selected from this region

Heating up reaction time Cooling down reaction time

Reaction time Measurement Results

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Starting heating here

• Run 3 has a large deviation with run 1,2,5 • Run 1 and run 5 have similar behavior • Run2 and run 3 somehow have similar behavior

Reaction Time Measurement Results

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• The reaction time for heating up the wire until response finished is about 1.49 seconds

• The reaction time for cooling down the wire until response finished is about 3.68 seconds

Run Heating up reaction Time(Sec) Cooling down reaction Time(Sec)

1 1.7667 3.1333

2 1.0000 4.2667

3 1.5333 3.4000

5 1.6667 3.9333

Mean 1.4917 3.6833

Conclusion and future work

Conclusion

• Clear relationship between temperature and hue has been demonstrated.

• This mathematical relationship can tell the temperature at wires for any random point by the color (hue) there.

• TLC is potentially a reliable temperature measurement technology .

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Future work • Redo the oven calibration using a black background for a clear vision • Find and test some other materials for the filaments to get a quicker

response • Find a suitable material for the window to observe in the blowdown wind

tunnel for temperature measurement

Acknowledgement

• Prof. Randall Mathison

• Dr. Igor Ilyin

• Mr. Kenneth Fout

• Mr. Timothy Lawler, Graduate student

• College of Engineering at The Ohio State University

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Thank you