Shadow Doppler technique for sizing particles of arbitrary shape

Abstract

The output from a linear diode array is used in a modified laser Doppler velocimeter to measure the size and shape of irregular particles. The sizing accuracy for transparent and opaque particles between 30 and 140 µm is better than 10%. The inaccuracy caused by trajectories that lay at angles of less than 24° to the axis of the array was less than +5%, and a further inaccuracy of +5% was caused by defocusing of the particle from the center of the velocimeter measuring volume by up to ±500 µm. The advantages of the shadow Doppler technique over other techniques for sizing irregular particles, such as amplitude systems with pointer volumes, are that the shadow Doppler technique records shape, the optical arrangement is more robust, less precise alignment is required, and the equipment can be constructed at low cost.

Two‐Phase Flow Characterization by Automated Digital Image Analysis. Part 1: Fundamental Principles and Calibration of the Technique

“…The lack of spatial resolution and sensitivity to beam attenuation are limitations of the laser diffraction technique. Another technique, shadow Doppler velocimetry (SDV), described by Hardalupas et al [9] is capable of measuring non-spherical, opaque and transparent particles however the limited dynamic range restricts the range of application of this particular method at present. An alternative technique for the measurement of droplet size is through direct imaging.…”

Shadow Doppler Velocimetry for Simultaneous Size and Velocity Measurements of Irregular Particles in Confined Reacting Flows

“…However, parti c les ge nerate no useful sizin g sig nal when their trajectory li es parallel to the ax is of the linear array and s izin g increases as the traj ecto ry a ng le approaches th e normal to the axis. The res ults of Hardalupas et al [ 15] show th at th e error of trajectory ang les abo ut ::' :: 30° to the no rm al to th e array ax is is a bout 7% for ve locities of th e o rd er of I m/s and it is no t ex pected to exceed I 0% for the ve loc iti es meas ured in thi s work, provided that particles at large (see below) o ut-of-focu s distances are rejected. For sma ll er angles this erro r fa ll s below 5% .…”

“…Thus the number of publication s whi c h re po rt a pplicati o ns o f o ptica ll y-based in strume nts fo r si111 ultaneous meas ure me nt of s ize and ve loc ity is sma ll beca use o f th e d iffi c ulty o r ma kin g the meas ure me nts with the amplitude o f diffl·acti ve ly-scatte red li g ht. Hardalupas et a l. [ 15) recentl y deve lo ped the Shadow Do ppl er Ye loc ime te r in strume nt whi c h has the po te nti a l to ma ke acc urate measure me nt s throu g h glass w indo w s w hil e ma inta ining a li g nm e nt o ver lo ng peri od s. The acc uracy of S OY was assessed in isothe rm a l fl ows by Morikita et a l. 11 6 ) who s howed th at th e max imum diffe re nce betwee n the arithme ti c mea n di a mete r of irreg ular particles a nd microsco pi c meas ure me nt was abo ut I 0 %. Hishida e t a l. [ 17) reco rded a maximum size unde res tim ati o n o f 4 %, o wing to beam wande rin g du e to te mpe ra ture g radie nts a nd they co nc luded th at th e max imum e rror w ith inc reas in g fl a me s ize canno t exceed 15 % , and a max imum syste mati c e rro r o f -12 % fo r a 25 1-Lm pinhole w ith li g ht co ll ected thro ugh a 15 mm w id e windo w .…”

Machine Vision Instrument to Measure Spray Droplet Sizes

“…The empirically determined threshold was applied to eliminate the out-of-focus droplets in the image. Thus, the droplet size distribution only includes the size data of well-focused droplets to minimize measurement error (Hardalupas et al, 1994;Kashdan et al, 2007). An example processing image set for detecting droplets is in fig.…”