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 22. Composition measurement 2 Composition measurement Sample analysis Orsat analyzer - classical, old-fashioned device - volume change measured after absorption of each gas - simple and inexpensive - manual, slow and tedious 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 from industrial plants - automatic systems including three main methods of sample analysis • absorb spectroscopy • luminescence techniques • electroalanalytical methods 3 Composition measurement Sample analysis Gas chromatography - method for separation and analysis of gas and volatile liquid mixtures signal output sample injection flow regulator detector column oven carrier gas - 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. - The substances having the greater interaction with the stationary phase are retarded to a greater extent and consequently separate from those with smaller interaction. - As the components elute from the column they can be quantified by a detector and/or collected for further analysis. 4 Composition measurement Sample analysis Gas chromatography 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. 5 Composition measurement Sample analysis Absorption spectrophotometry Light absorption following Beer’s law: For two or more types of molecules: I0 – radiant intensity of incident light I – radiant intensity of passing light ļ„ – molar absorptivity coefficient l – length of path C – concentration 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 6 Composition measurement Sample analysis Mass spectrometry - utilize electric and magnetic fields to separate ions according to mass and charge 7 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 8 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 Rayleigh-scattering methods - used to measure local concentration of chemical species in pure gas Many other related & similar methods 9 Homework - Read textbook 13.1-13.4 on page 307 - 316 - Questions and Problems: 1 on page 323 n ļ1 ļ½ Kļ² š¾ = š¾1 š1 + š¾2 š2 /ļ² ļ²1+ļ²2=ļ² ?? - Due on 10/17 10 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 Sx Sy]=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 Sx = -2.2969 Sy = 2.1598 11 Learn to write a Matlab program • to select an image sample in a 64×64-pixel window from a double exposed PIV recording at x=400, y=200 Mean removed http://lcgui.net/ui-lecture2012/hw/00/D001_1.BMP • to remove mean gray values of the image sample • to determine auto-correlation function Mean not removed 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'); 12