Measurements in Fluid Mechanics058:180 (ME:5180)

Time & Location: 2:30P - 3:20P MWF 3315 SC

Office Hours: 4:00P – 5:00P MWF 223B-5 HL

Instructor: Lichuan Guilichuan-gui@uiowa.edu

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

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Lecture 22. Composition measurement

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Composition measurement

Sample analysisOrsat analyzer- classical, old-fashioned device

- simple and inexpensive

- manual, slow and tedious

- volume change measured after absorption of each gas

Electronic testers- contain electrochemical gas sensors, each measuring the concentration of a particular type of molecule.

Continuous-emission monitoring systems (CEMs)

- continuous monitoring of exhaust gas fromindustrial plants

• absorb spectroscopy

• luminescence techniques

• electroalanalytical methods

- automatic systems including three main methods of sample analysis

4- As the components elute from the column they can be quantified by a detector and/or collected for further

analysis.

carrier gas

flow regulator

sample injection

column oven

detector

signal output

- The substances having the greater interaction with the stationary phase are retarded to a greater extent and consequently separate from those with smaller interaction.

Composition measurement

Gas chromatography - method for separation and analysis of gas and volatile liquid mixtures

- A small gas sample is injected into a stream of an inert carrier gas, e.g. helium or nitrogen (liquid samples are vaporized before injection into the carrier stream)

- The gas stream is passed through the packed column, through which the components of the sample move at velocities that are influenced by the degree of interaction of each constituent with the stationary nonvolatile phase.

Sample analysis

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Composition measurement

Typical chromatogram

- appears as a sequence of peaks, each associated with a gas component and separated by specific time intervals.

- the components of the gas mixture in the test sample are identified by timing of the peaks.

- the concentrations of the identified components can be found by measurement of the areas under each peak.

Gas chromatographySample analysis

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Composition measurement

Absorption spectrophotometry Sample analysis

Light absorption following Beer’s law: I – radiant intensity of passing lightI0 – radiant intensity of incident light

– molar absorptivity coefficientl – length of pathC – concentration of moleculesFor two or more types of molecules:

- A particular molecule can be identified by analyzing spectrum of the absorbed radiation because each type of molecule absorbs radiation at particular wavelengths

- Concentrations of gas mixture components can be determined by radiation of different wavelengths

Example of absorption spectrophotometry

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Composition measurement

Mass spectrometry Sample analysis

- utilize electric and magnetic fields to separate ions according to mass and charge

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Composition measurement

Thermal probes

- thermal conductivity of a fluid mixture depends on the mass fractions of its constituents.

- the composition of a binary mixture of fluids can be estimated from heat transfer measurements by use of thermal sensors.

Interfering thermal probe

- two hot-wire-hot-film sensors

Aspirating thermal probe

- thermal sensor inside small sampling tube

Electric conductivity probes- used to measure local concentration of electrolyte in liquid solution according to electric resistance

of a path between two electrodes

- single-electrode type sensors commonly used

- calibration in liquid solutions with known uniform concentrations of electrolyte

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Composition measurement

Light-scattering methods

Basic experimental arrangement

- laser beam or other collimated beam of light

- focused on measuring volume of 1 mm3 or less

- scattered light collected by collecting lens

- separated from other radiation with slit or pinhole

- projected to photodetector for subsequent analysis

Mie-scattering methods

- used to measure local concentration of smoke or mists contained in gases

Many other related & similar methods

Rayleigh-scattering methods

- used to measure local concentration of chemical species in pure gas

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Homework

- Questions and Problems: 1 on page 323- Read textbook 13.1-13.4 on page 307 - 316

- Due on 10/17

Kn 1

1+2=

𝐾=(𝐾1 𝜌1+𝐾 2𝜌 2) /

??

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

Learn to write a Matlab program

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

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 Sx Sy]=peaksearch(c,20)C=xy2img(c);imwrite(C,'C.bmp','bmp');

• to remove mean gray values of the 2 image samples• to determine cross-correlation function

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

• to determine particle image displacement

Sx = -2.2969

Sy = 2.1598

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• to select an image sample in a 64×64-pixel window from a double exposed PIV recording at x=400, y=200

Learn to write a Matlab program

http://lcgui.net/ui-lecture2012/hw/00/D001_1.BMP

• to remove mean gray values of the image sample• to determine auto-correlation function

clear;D1=imread('D001_1.bmp'); G1=img2xy(D1);M=64; N=64; x=400;y=200;g1=sample01(D1,M,N,x,y);g1=g1-mean(mean(g1));c=xcorr2(g1,g1);C=xy2img(c);imwrite(C,'C.bmp','bmp');

Mean removed Mean not removed