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Published in Bahram Nassersharif, Engineering Capstone Design, 2022
The same cameras used for photography can typically be used for videography. Videography adds the dimension of time to the event being captured. The timeline captured in a video can be used to make calculations that are time-dependent such as a process timing study, measuring position, velocity, and acceleration.
Ignition and Combustion Characteristics of Al/RDX/NC Nanostructured Microparticles
Published in Combustion Science and Technology, 2021
Gregory Young, Daniel P. Wilson, Michael Kessler, Jeffery B. DeLisio, Michael R. Zachariah
Two types of ignition experiments were conducted in this study. The first used our high pressure T-jump which has been described elsewhere (Young, Roberts, Stoltz 2015b; Young, Wang, Zachariah 2015c). Briefly, particles were deposited on a 75 μm platinum filament and placed in an optically accessible pressure vessel. The pressure vessel had three quartz windows available for observing the experiments. A voltage is quickly applied across the platinum filament causing it to be resistively heated, leading to an ignition event for a given sample. The heating rate used during the T-jump experiments in this study was approximately 100,000 K/s. During the experiments the platinum filament was heated from room temperature to in excess of 1000 K at which point any and all reactions that were expected would have been completed. Experiments were conducted with either air or nitrogen used as the pressurizing gas up to about 5.17 MPa. High speed videography was conducted using a Phantom 7.10 high speed camera to image the ignition events. Framing rates of 5000 frames per second and exposure times of 5 μs or 200 μs were used depending on whether or not any lighting was used to conduct shadowgraph imaging during the experiment. For shadowgraph imaging, a 250 Watt halogen light was used for backlighting the experiment. The reference time in the images, t0, refers to the first instance in which a reaction is detected in the video sequence.
Towards an evaluation of bedload transport characteristics by using Doppler and backscatter outputs from ADCPs
Published in Journal of Hydraulic Research, 2021
Slaven Conevski, Massimo Guerrero, Colin D. Rennie, Nils Ruther
Beside the image velocity data (vc), the instantaneous values of mean surface bedload concentration (Km) were also determined using the planar videography (Conevski et al., 2019). No specific ROI was chosen to calculate Km, but it was simply determined as an average value of all the available ROI in the FOV. It is well known that the motion of the gravel particles is rather heterogeneous and sporadic, which resulted in no transport in some parts of the flume and very intense bedload transport in some others. This heterogeneity affected the Km. Therefore, the resulting ROIs with zero and values smaller than 0.001 were discarded, which defined the active bedload surface concentration, Kact, for gravel experiments. The Kact values were verified by calculating the total surface of the identified particles assuming a circular shape. For the sand experiments, all ROI showed similar values of the bedload surface concentration, resulting in Kact = Km. Note that for the ADCPs data, the zero velocities were automatically discarded (e.g. N/A values) or produced negative values.
Experimental study of bubble departure characteristics in forced convective subcooled nucleate boiling
Published in Experimental Heat Transfer, 2018
Parul Goel, Arun K. Nayak, Pradyumna Ghosh, Jyeshtharaj B. Joshi
Sugrue [23] studied the effect of heater orientation angle, subcooling, heat flux, mass flux, and pressure on bubble departure diameter and compared the results with the mechanistic model of Klausner et al. [24]. He observed that the departure diameter increased with increasing heat flux, decreasing degree of subcooling, decreasing mass flux, and decreasing pressure. His observations also showed that the largest bubbles departed from the downward-facing horizontal heater (inclination angle of 0) and smallest bubbles from a vertical heater (angle 90). They compared their results with the Klausner model which gave good qualitative agreement with reference to behavior of diameter with thermal conditions but showed substantial quantitative errors. Phillips [25] studied subcooled flow boiling using synchronized high-speed videography, IR thermography, and Particle Image Velocimetry (PIV) imaging techniques on a similar set-up. He recorded that the heat transfer coefficient increased with an increase in mass flux in the single-phase region, but was less affected by heat flux at a given mass flux. When boiling began, the heat transfer coefficient increased considerably and the different mass flux curves merged for high heat flux values. The bubble departure diameter trends with heat flux, mass flux, pressure, and subcooling were like those observed by Sugrue [23]. He measured the departure frequency under different conditions and observed that the departure frequency increased with an increase in the heat flux, degree of subcooling, and pressure and decreased with an increase in the liquid velocity. He compared the experimental results for departure frequency with the models of Podowski and Podowski [26], Yeoh et al. [27], and Basu et al. [28] and found that the models could predict the growth time adequately but not the waiting time, and hence, the frequency was overpredicted. Guan et al. [29] in their subcooled boiling experiments at atmospheric pressure observed that the bubble departure diameter increased with an increase in heat flux, albeit slightly, but decreased with an increase in the degree of subcooling or mass flux. Based on their experiments, they proposed the bubble contact diameter as a logarithmic function of bubble diameter, since the contact diameter of the bubble would change with bubble growth.