Results Of High-speed Photography Research Articles

Non-contact measurement and experimental study on complex dynamic motion under high impact

The multiple impact equipment of short interval and multiple impact loading is the key equipment to verify the high impact resistance and initiation control strategy for multi-layer penetration fuze in laboratory, the motion law of the moving part under high impact has an important influence on the consistency of acceleration. In view of measurement problem of complex dynamic motion process under multiple high impact, a non-contact measurement method based on high-speed photography and image processing was presented, obtaining pixel coordinate of feature point of the moving part by background difference and feature point detection, combining with the sub-pixel algorithm, further improving the accuracy of measurement. The results of high-speed photography were verified by contrast experiment and dynamic simulation, proving that the method is reasonable and feasible for complex dynamic motion process measurement under high impact, providing support for optimal design of the multiple impact equipment, also enriching the existing methods of complex dynamic motion measurement.

Design of an active seed throwing and cleaning unit for pneumatic rice seed metering device

To address the clogging of the rice seed metering device after a long period of operation without affecting the precision of normal seeding, an active seed throwing and cleaning unit was designed based on the fact that magnets of the same pole were mutually exclusive. The working principle of the two devices was analysed theoretically, and a mechanical model was created according to the relationship between the repulsion forces of magnets and the spring forces of springs. The super hybrid rice Y-2 You 900 with 22.5% moisture content (wet basis) was used as the test object. The whole factor experiments were carried out under different negative pressures, rotational speeds of the suction plates, and lengths of probes. The results indicated that under any test conditions, the active seed throwing and cleaning unit worked normally. The results of high-speed photography showed that the rate of seed cleaning was 100%. The results also showed that the optimal negative pressure was 0.8 kPa. The probability of 1-3 seeds per hill for the seed metering device was approximately 95% under the optimal negative pressure. The optimal length of the probe was found to be 2 mm. The average qualified rate of hill space was 96.04% under the optimal length of probe, the longer the length of the probe, the lower the qualified rate of hill space. It also showed that an active seed throwing and cleaning unit could effectively avoid the hole clogging caused by the long-term operation and had no influence on the normal operation of the pneumatic rice seed metering device. The active seed throwing and cleaning unit improved the stability of the seed metering device, and the research provided a reference for the optimal design of seed throwing and cleaning structures of the pneumatic rice seed metering device. Keywords: agricultural machinery, seed metering device, seed cleaning, anti-clogging, pneumatic seed metering, precision seeder DOI: 10.25165/j.ijabe.20181102.3844 Citation: Xing H, Wang Z M, Luo X W, Zang Y, Yang W W, Zhang M H, et al. Design of an active seed throwing and cleaning unit for pneumatic rice seed metering device. Int J Agric & Biol Eng, 2018; 11(2): 62–69.

Using fast moving electrode to achieve overvoltage breakdown of gas switch stressed with high direct voltages.

A small-scale fast risetime gas switch attached to a 50 Ω pulse forming line is tested. It includes a fast moving electrode and a fixed electrode. For the applied direct voltages, such as 2.8 kV, 2.0 kV, and 1.0 kV, the risetimes of this switch are tested to be ∼3.8 ns, ∼2.3 ns, and ∼1.1 ns, respectively, while the risetimes of a switch with two fixed electrodes are about ∼10.1 ns, ∼9.0 ns, and ∼3.6 ns. The results of high-speed photography and laser interferometry reveal that the moving electrode will obviously shorten discharge spark length but almost will not change the inter-electrodes gas pressure. The reason of shortening spark length is the existence of the discharge time delay of gas switch. After moving to the static breakdown spacing, the fast moving electrode will move on for an additional distance within the discharge time delay, which makes gas switch achieve overvoltage breakdown under high direct voltages and therefore leads to shorter spark length and faster switch risetime.

Quantitative Evaluation of Heat Transfer in Bubble Collapse Process in Subcooled Flow Boiling

In this paper an attempt has been made to quantitatively determine the heat transfer contribution of the different mechanisms during the bubble collapse process in subcooled flow boiling condition.For achieving this objective, the bubble behavior was studied during the subcooled flow boiling on a vertical heating rod with upward coolant water using the results of high-speed photography obtained by Nematollahi in 1999 at Tohoku University. Subsequently, some parameters including superheated layer thickness and active nucleation sites density as well as bubble parameter such as maximum diameter, life time, generation period and so forth were measured for calculation purpose of this study.In the present investigation, four procedures of superheated layer mixing, turbulence induced by bubble collapse phenomenon, latent heat transport and transferring the energy by stable micro bubbles (SMB) (remained after original bubble collapse) were considered as the bubble mechanisms during the collapse process in subcooled flow boiling. Consequently, the heat transfer contributions of the bubble mechanisms were calculated using the applied models in the literature as well as the results obtained from the bubble behavior analysis for different experimental conditions of inlet subcooled temperature, linear power density (W/cm), flow velocity as well as two heights of a heated rod.According to the calculated results, the most effective mechanism of heat transfer during the bubble collapse process was nominated to be superheated layer mixing at the moment of bubble departure with contribution ranging from 2.62% to 34.11% and average value of 9.8% to total heat flux. Also it was concluded that an average value of about 18% from total heat flux is transferred during the condensation of bubble, as it starts to shrink and finally collapses in the subcooled liquid at the end of its life in the subcooled flow boiling.

Experimental Study and Numerical Modeling of Keyhole Behavior during CO2 Laser Welding

The present paper describes the results of high speed photography, acoustic emission (AE) detection and plasma light emission (LE) measurement during CO₂ laser welding of 304 stainless steel in different processing conditions. Video images with high spatial and temporal resolution allowed to observe the melt dynamics and keyhole evolution. The existence of keyhole was confirmed by the slag motion on the weld pool. The characteristic frequencies of flow instability and keyhole fluctuations at different welding speed were measured and compared with the results of Fourier analyses of temporal AE and LE spectra. The experimental results were compared with the newly developed numerical model of keyhole dynamics. The model is based on the assumption that the propagation of front part of keyhole into material is due to the melt ejection driven by laser induced surface evaporation. The calculations predict that a high speed melt flow is induced at the front part of keyhole when the sample travel speed exceeds several 10 ㎜/s. The numerical analysis also shows the hump formation on the front keyhole wall surface. Experimentally observed melt behavior and transformation of the AE and LE spectra with variation of welding speed are qualitatively in good agreement with the model predictions.

Dynamic and structural aspects of the processes of single-phase convective heat transfer metastable regime decay and bubble boiling formation

This paper is concerned with the study of the mechanism underlying the formation of the bubble boiling regime on the surface of a heat generating element. Investigations are carried out on electrically heated platinum wires placed in different hydrocarbons. The process of transition from convection to boiling was induced by local disturbances in the region of metastability. It has been found that under the conditions described a self-wave-type transition process is initiated. Depending on the depth of the penetration into the metastability region, the transition process may take place in two modes—of slow and fast waves—that differ by the velocity scale and front structure. The relationships between the wave velocity and the temperature of the heating element have been obtained. Possible mechanisms of the self-wave transition process are considered. The process is found to be identical with the detonation phenomenon. The results obtained are extended to the case of steady-state bubble boiling of subcooled liquid. It is concluded that under the conditions considered the bubble boiling constitutes a poly-self-wave process, i.e. the superposition of fast and slow self-wave processes taking place simultaneously on the heater. The major conclusions are confirmed by the results of high-speed photography.