Instructor: Lichuan Gui lichuan-gui@uiowa

1. 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

2. Lecture 21. Temperature measurement

3. 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 Celsius, or centigrade, scale - 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

4. Temperature measurement 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

5. Temperature measurement 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

6. Temperature measurement 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

7. Temperature measurement 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

8. Temperature measurement 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

9. Temperature measurement Thermocouples Sensor & measuring circuit

10. Temperature measurement 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

11. Homework - Read textbook 12.1-12.2 on page 290 - 296 • Questions and Problems: 6 on page 305 - Due on 10/15

12. 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; A1=imread('A001_1.bmp'); A2=imread('A001_2.bmp'); 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