Ala Hijazi

Bio: Ala Hijazi is an academic researcher from German-Jordanian University. The author has contributed to research in topics: Digital image correlation & Residual strength. The author has an hindex of 9, co-authored 24 publications receiving 684 citations. Previous affiliations of Ala Hijazi include Hashemite University & Wichita State University.

System and method for capturing image sequences at ultra-high framing rates

Abstract: An imaging system for capturing a sequence of images from a target at ultra-high framing rates is disclosed. The imaging system includes an illumination system operable to emit at least first and second light pulses at first and second wavelengths, respectively. The first and second light pulses sequentially illuminate the target whereupon at least first and second propagated light pulses emanate from the target. The system also includes at least first and second image sensors operable to receive the first and second propagated light pulses, respectively, to thereby capture the sequence of images from the target. Various exemplary embodiments of the imaging system and associated method are provided.

A novel ultra-high speed camera for digital image processing applications

Abstract: Multi-channel gated-intensified cameras are commonly used for capturing images at ultra-high frame rates. The use of image intensifiers reduces the image resolution and increases the error in applications requiring high-quality images, such as digital image correlation. We report the development of a new type of non-intensified multi-channel camera system that permits recording of image sequences at ultra-high frame rates at the native resolution afforded by the imaging optics and the cameras used. This camera system is based upon the concept of using a sequence of short-duration light pulses of different wavelengths for illumination and using wavelength selective elements in the imaging system to route each particular wavelength of light to a particular camera. As such, the duration of the light pulses controls the exposure time and the timing of the light pulses controls the interframe time. A prototype camera system built according to this concept comprises four dual-frame cameras synchronized with four dual-cavity pulsed lasers producing 5 ns pulses in four different wavelengths. The prototype is capable of recording four-frame full-resolution image sequences at frame rates up to 200 MHz and eight-frame image sequences at frame rates up to 8 MHz. This system is built around a stereo microscope to capture stereoscopic image sequences usable for 3D digital image correlation. The camera system is used for imaging the chip‐workpiece interface area during high speed machining, and the images are used to map the strain rate in the primary shear zone.

A calibrated dual-wavelength infrared thermometry approach with non-greybody compensation for machining temperature measurements

Abstract: We report the development of a new approach for determining temperatures using the dual-wavelength infrared thermometry technique, which does not presume greybody behaviour and compensates for the spectral dependence of emissivity. This approach is based on Planck's radiation equation and explicitly accounts for the wavelength-dependent response of the IR detector and the losses occurring due to each of the elements of the IR imaging system that affect the total radiant energy sensed in different spectral bands. A thorough calibration procedure is utilized to determine a compensation factor for the spectral dependence of emissivity, which is referred to as the non-greybody compensation factor (NGCF). Calibration and validation experiments are carried out on Aluminum 6061-T6 targets with two different surface roughnesses. Results show that this alloy does not exhibit greybody behaviour, even though the two spectral bands used were relatively close to each other, and that the spectral dependence of emissivity is influenced by the surface finish. It is found that non-greybody behaviour of low emissivity surfaces can lead to significant systematic error in dual-wavelength IR thermometry. The inclusion of the NGCF eliminates the systematic error caused by the invalidity of greybody assumption and thus improves the accuracy of the measurements. Non-greybody-compensated dual-wavelength thermography is used to measure the chip temperature along the tool–chip interface during orthogonal cutting of Al 6061-T6 and sample results at three different cutting speeds are presented.

Random Data Analysis And Measurement Procedures

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A review on nanofluids - Part I: Theoretical and numerical investigations

Abstract: Research in convective heat transfer using suspensions of nanometer-sized solid particles in base liquids started only over the past decade. Recent investigations on nanofluids, as such suspensions are often called, indicate that the suspended nanoparticles markedly change the transport properties and heat transfer characteristics of the suspension. This first part of the review summarizes recent research on theoretical and numerical investigations of various thermal properties and applications of nanofluids.

Natural convection cooling of a localised heat source at the bottom of a nanofluid-filled enclosure

Abstract: This article presents a numerical study of natural convection cooling of a heat source embedded on the bottom wall of an enclosure filled with nanofluids. The top and vertical walls of the enclosure are maintained at a relatively low temperature. The transport equations for a Newtonian fluid are solved numerically with a finite volume approach using the SIMPLE algorithm. The influence of pertinent parameters such as Rayleigh number, location and geometry of the heat source, the type of nanofluid and solid volume fraction of nanoparticles on the cooling performance is studied. The results indicate that adding nanoparticles into pure water improves its cooling performance especially at low Rayleigh numbers. The type of nanoparticles and the length and location of the heat source proved to significantly affect the heat source maximum temperature.