High-speed Digital Imaging System Research Articles

A high-speed digital imaging system for recording non-repetitive transient events

A high-speed digital imaging system employing electronic controls and standard optical elements has been developed. A cavity-dumped argon laser is used to provide very short duration monochromatic light pulses with short interpulse times, while an acousto-optic deflector provides spatial separation of each image. Electronic solid-state imaging is accomplished with charge injection device cameras. Full frame images (512 × 512 pixels) of the actual light intensity variations in the imaged object are digitally recorded to a resolution of 256 gray levels using a frame grabber and a host computer. This system has applications m the study of high-speed phenomena, such as dynamic fracture, impact mechanics and fluid flow.

Techniques for high-speed digital imaging of gas concentrations in turbulent flows

Techniques have been developed to measure the concentration of nozzle gas quantitatively in transitional and turbulent flow regimes at high framing rates in two dimensions. Elastically scattered light from a seeded jet, illuminated by a sheet of laser light, was recorded in three ways. The first involved the use of a rotating mirror to sequentially place images onto different portions of a relatively slow vidicon-based imaging system to achieve a high effective framing rate (2–10 kHz) for up to four frames. The second used a portion of a monolithic 128×128 photodiode array connected directly to a high-speed analog to digital converter to achieve a framing rate of 1.136 kHz. The third used a fast video camera and recorder (6 kHz) to store images on magnetic tape in analog form, which were later digitized upon playback. A comparison of these techniques is presented along with a discussion of factors important in the use of high-speed digital imaging systems. It is shown that the temporal development of large-scale structures can be digitally recorded in two dimensions, with the advantage of being both quantitative and visually interpretable.

The effect of thyroid therapy on children: Anne Topper and Philip Cohen. Am. Jour. Dis. Child., February, 1928, xxxv, 2

Spray formation is important for liquid fuel combustion from the perspective of emissions and sustaining combustion. Employing swirl flow increases turbulent intensity, which leads to a much-desired outcome for sprays in a reduction of the jet breakup length, better air-fuel mixing and vaporization characteristics, and stabilizes the combustion operation. The present investigation endeavors to characterize the near field spray developing region of a swirl airblast atomizer. The high-speed digital imaging system is employed to record the unsteady dynamics when the liquid jet breaks to form mono-disperse or poly-disperse drop size distribution depending upon the atomizing air to liquid jet momentum ratio. The coherent spatial nature of the atomization process is identified using Proper Orthogonal Decomposition (POD) of acquired high-speed images of the spray in the near field. The simultaneous droplet size and velocities (axial, radial, and tangential) are measured through Phase Doppler Particle Analyzer (PDPA) technique to quantify the effect of the flow field on spray characteristics in the near field of an atomizer. Joint probability distributions of drop size and velocity along with Weber number distribution provide insight into the spray developing near field region. The spatial variations in the drop size distribution are found to be a function of turbulent Weber number (Wet) and shear Weber number (Wes) distribution. Double Gaussian function representing superimposed distributions for larger and smaller droplets provides the highest confidence fit for both velocity and dropsize distributions throughout the flow field. The volume-averaged statistics are proposed for a better description of the actual spray quality.