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# Instructor: Lichuan Gui lichuan-gui@uiowa - PowerPoint PPT Presentation

Measurements in Fluid Mechanics 058:180 ( ME:5180 ) Time & Location: 2:30P - 3:20P MWF 3315 SC Office Hours: 4:00P – 5:00P MWF 223B -5 HL. Instructor: Lichuan Gui lichuan-gui@uiowa.edu Phone: 319-384-0594 (Lab), 319-400-5985 ( Cell) http:// lcgui.net. Lecture 21. Temperature measurement.

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Instructor: Lichuan Gui lichuan-gui@uiowa

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Measurements in Fluid Mechanics058:180 (ME:5180)Time & Location: 2:30P - 3:20P MWF 3315 SCOffice Hours: 4:00P – 5:00P MWF 223B-5 HL

Instructor: Lichuan Gui

lichuan-gui@uiowa.edu

Phone: 319-384-0594 (Lab), 319-400-5985 (Cell) http://lcgui.net

Lecture 21. Temperature measurement

Temperature scales

- three temperature scales in use today, Fahrenheit (F), Celsius (C) and Kelvin (K)

Fahrenheit temperature scale

- 32 for the freezing point of water

- 212 for the boiling point of water

- interval divided into 180 parts

- 0 for the freezing point of water

- 100 for the boiling point of water

- conversion formula: F = 9/5C + 32

Kelvin temperature scale

- base unit in International System (SI) of measurement

- zero point at absolute zero

- difference between the freezing and boiling points of water is 100 degrees

- conversion formula: K = C + 273

Thermometers

Thermal expansion thermometers

- liquid-in-glass thermometers

- bimetallic thermometers

Thermocouples

- based on the thermoelectric effect

Resistance thermometers

- based on the relationship between temperature and electric resistance

- include metallic resistance sensors (RTDs), and semiconductor resistance sensors

Coil elements

Liquid-in-glass thermometers

- a bulb, a reservoir in which the working liquid can expand or contract in volume

- a stem, a glass tube containing a tiny capillary connected to the bulb and enlarged at the bottom into a bulb that is partially filled with a working liquid. The tube's bore is extremely small - less than 0.5 mm in diameter

- a temperature scale is fixed or engraved on the stem supporting the capillary tube to indicate the range and the value of the temperature. The liquid-in-glass thermometers is usually calibrated against a standard thermometer and at the melting point of water

- a reference point, a calibration point, the most common being the ice point

- a working liquid, usually mercury or alcohol

- an inert gas is used for mercury intended to high temperature. The thermometer is filled with an inert gas such as argon or nitrogen above the mercury to reduce its volatilization.

- constriction may be used to measure maximal or minimal temperature

Liquid-in-glass thermometers

- Typical resolution: 0.05-1 K

- Immersion types:partial Immersion (inserted in fluid up to marked line) total immersion (inserted in fluid up to liquid column) complete immersion (entirely immersed in fluid)

- total immersion required to avoid errors due to temperature difference between immersed and non-immersed sections

- stem correction necessary with partial immersion thermometers

e.g. for mercury-in-glass thermometers:

- number of degrees (K) of the non-immersed portion

- temperature of the immersed portion

- temperature of the non-immersed portion

- disadvantage: poor spatial and temporal resolutions

- advantage: excellent laboratory standards for calibration of other instruments

Bimetallic thermometers

- two thin plates of different materials

- vastly different thermal expansion coefficient

- bonded together tightly with one end fixed & another free

- curvature of the assembly changed due to temperature variation

- helically or spiral coiled assembly used to amplify motion resulting from temperature change

Bimetallic thermometer (flat, spiral strip)

- bimetallic assemblies also used in thermostatic controls

- typical resolution about 1% of full scale, and maximal operation temperature around 500C

Thermocouples

Seebeck effect

- Any electrical conductor will develop a potential difference (thermoelectric voltage) between two of its points that have a temperature difference.

Thermocouple configuration

- two dissimilar metallic wires (e.g. A and B) joined firmly at two junctions

- one junction exposed to the temperature of interest (e.g. T1)

- the other one (reference junction) kept at known constant temperature (e.g. T2)

- reference junction conventionally immersed in an ice bath for reference temperature of 0C

- constant reference temperature also provided with an electronically controlled heated block

- common types of thermocouples and their properties

- typical resolution in the order of 1C

- highest temperature of 2930C by tungsten-rhenium type

Thermocouples

Sensor & measuring circuit

Resistance thermometers

Resistance temperature detectors (RTDs)

- pure metal thermometers of platinum (most popular and accurate), nickel, or copper

- typical resolution of 0.1 K, possible high resolution of 0.0001 K

- non-linear response fitted with low-order polynomials e.g. resistance Rpt of platinum RTD in the range 0f 100-700C described by Callendar-Van Dusen equation

Rpt0 – resistance at 0C

Cold-wires

- similar construction to HW

- high frequency response in temperature measurement

Thermistors

- semiconductor elements whose resistance is a very strong function of temperature.

- extremely high sensitivity to temperature

- non-linear response

- Read textbook 12.1-12.2 on page 290 - 296

• Questions and Problems: 6 on page 305

- Due on 10/15

Learn to write a Matlab program

• to select image samples in a 32×32-pixel window from two images at x=400, y=200

Example of Matlab program:

clear;

G1=img2xy(A1);

G2=img2xy(A2);

M=32;

N=32;

x=400;

y=200;

g1=sample01(G1,M,N,x,y);

g2=sample01(G2,M,N,x,y);

g1=g1-mean(mean(g1));

g2=g2-mean(mean(g2));

c=xcorr2(g1,g2);

[cm SxSy]=peaksearch(c,20)

C=xy2img(c);

imwrite(C,'C.bmp','bmp');

http://lcgui.net/ui-lecture2012/hw/00/A001_1.BMP

http://lcgui.net/ui-lecture2012/hw/00/A001_2.BMP

• to remove mean gray values of the 2 image samples

• to determine cross-correlation function

• to determine particle image displacement