1 / 16

Instructor: Lichuan Gui lichuan-gui@uiowa

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 15. Flow rate measurement.

tamal
Télécharger la présentation

Instructor: Lichuan Gui lichuan-gui@uiowa

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  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 15. Flow rate measurement

  3. Flow rate measurement Averaging Pitot tubes - a tube spanning the cross section of the pipe - multiple frontal openings for averaged total pressure - second tube facing backwards to measure static pressure

  4. Flow rate measurement Laminar flow elements - contain tube bundles or long honeycombs - create laminar flow with Re<2300 - linear response between flow rate and pressure drop

  5. Flow rate measurement Rotameters (variable-area flow meters) - vertical tube with cross section increasing linearly upwards - a float at a position with drag, buoyancy and weight in balance - height of float proportional to flow rate

  6. Flow rate measurement Vortex-shedding flow meters - a bluff object results in periodic shedding of vortices - vibration frequency (f) measured downstream - constant Strouhal number with Re>5000: - flow velocity determined by h – front width of the bluff V – flow velocity - S=0.14-0.21, dependent on shape of the bluff body - flow rate given as k – constant depending on the structure Drag (target) flow meters - bluff object immersed in flow - drag force FD measured

  7. Flow rate measurement Turbine flow meters - an immersed rotor with vanes - angular velocity measured with pulse counter - flow rate proportional to angular velocity k – constant n – number of pulses per unit time Paddle-wheel flow meters - axis normal to flow direction

  8. Flow rate measurement Ultrasonic flow meters - use sound waves to measure flow rate of fluid Doppler flow meters - 2 piezoelectric crystals: transmitter & receiver - solid particles or gas bubbles reflect ultrasound - frequency difference used to determine velocity ft – transmitted frequency - Doppler shift: fr – received frequency c – sound speed  – measurement angle Time-of-flight flow meters - Two pairs of transmitter & receiver - located upstream and downstream - sound pulse transported by flowing fluid - frequency change used to calculate flow velocity l – distance between transducers - independent of sound speed (temperature)

  9. Flow rate measurement Electromagnetic (magnetic, induction) flow meters - conductive fluid passing across a controlled magnetic field - flow velocity obtained by measuring changes of induced voltage - flow rate determined accordingly E – electric potential k – numerical coeficient D – pipe diameter B – magnetic flux density Coriolis flow meters - flow guided into U-shaped tube - twist induced to the tube by Coriolisacceleration - time delay t between motions of two legs measured - mass flow rate related as rt– radius of the tube KS– constant

  10. Flow rate measurement Thermal flow meters Heated-tube flow meters - flowing gas passed electrically heated tube - temperature measured up- and down stream - heat transfer rate related to mass flow rate Cp – specific heat under constant pressure Immersion-probe flow meters - two resistance temperature detectors (RTDs) - one RTD used to measure gas temperature - another heated with current to higher temperature - electric power related non-linearly to V

  11. Flow rate measurement Selection of flow meters

  12. Homework - Read textbook 9.5-9.15 on page 212 - 219 • Questions and Problems: 2 on page 219 - Due on 10/01

  13. Learn to write a Matlab program • Matlab function for transferring image coordinate (i,j) to physical coordinates (x,y) nx – number of columns , ny – number of lines x = ny-j+1, y=i y j function [G]=img2xy(A) % A - image % G - gray value distribution [nynx]=size(A); for x=1:nx for y=1:ny G(x,y)=A(ny-y+1,x); end end x http://lcgui.net/ui-lecture2012/hw/00/A001_1.BMP i

  14. Learn to write a Matlab program • Matlab function for transferring physical coordinates (x,y) to image coordinate (i,j) nx – number of columns , ny – number of lines j=ny-x+1, i=y function [A]=xy2img(G) % A - image % G - gray value distribution [nxny]=size(G); Gmax=max(max(G)); Gmin=min(min(G)); for x=1:nx for y=1:ny A(ny-y+1,x)=uint8(double(G(x,y)-Gmin)/double(Gmax-Gmin)*245+5); end end

  15. Matlab function for selecting an interrogation sample from an image for i=1:M for j=1:N ii=i+I-int16(M/2); jj=j+J-int16(N/2); if ii>=1 & ii<nx & jj>=1 & jj<ny Ga=double(G(ii,jj)); Gb=double(G(ii+1,jj)); Gc=double(G(ii,jj+1)); Gd=double(G(ii+1,jj+1)); A=(1-x)*(1-y); B=x*(1-y); C=(1-x)*y; D=x*y; g(i,j)=A*Ga+B*Gb+C*Gc+D*Gd; % bilinear interpolation gm=gm+g(i,j); nr=nr+1; else g(i,j)=-1; end end end gm=gm/double(nr); for i=1:M for j=1:N if g(i,j)<0 g(i,j)=gm; end end end function[g]=sample01(G,M,N,X,Y) %INPUT PARAMETERS % G - gray value distribution of the PIV recording % M - interrogation sample width % N - interrogation sample height % X, Y - interrogation samplecoordinates % ---------------------------------------------------- % OUTPUT PARAMETERS % g - gray value distribution of the evaluation sample % ---------------------------------------------------- % I, J – integer part of evaluation sample coordinates % x,y – decimal part of evaluation sample coordinates [nxny]=size(G); I=int16(X); J=int16(Y); x=double(X)-double(I); y=double(Y)-double(J); if x<0 I=I-1; x=x+1; end if y<0 J=J-1; y=y+1; end gm=0; nr=0;

  16. Learn to write a Matlab program • To cut a 64×64-pixel image sample from a 1280×1024-pixel image at X=400.6, Y=200.3 64×64-pixel image sample clear; A1=imread('A001_1.bmp'); G1=img2xy(A1); M=64; N=64; x=400.6; y=200.3; g1=sample01(G1,M,N,x,y); A2=xy2img(g1) imwrite(A2,'G2.bmp','bmp') http://lcgui.net/ui-lecture2012/hw/00/A001_1.BMP 16

More Related