Influence of the Droplet Velocity on the Attenuation of Overpressures in a Water Mist

Mist generator is a basic element of systems designed to protect from explosions. It is responsible for forming a suppression barrier between the place of explosion and the zone to be protected. The effectiveness of the system is determined by the capacity of the mist to suppress blast overpressure and impulse. The attenuation capacity, on its turn, depends on mist properties, such as droplet size, water concentration in mist and droplet velocity. The paper examines droplet velocity influence on overpressure and impulse attenuation in mist when the properties of the latter are in the following ranges: droplet size - 15-345 μm; droplet velocity - 5.5-35 m/s; shock wave velocity – 515-718 m/s, droplet impact angle - 900. The influence of drop velocity on blast attenuation has been assessed according to overpressure and impulse reduction factors.

Evaluation of multiple precipitation sensor designs for precipitation rate and depth, drop size and velocity distribution, and precipitation type.

Observations of the precipitation rate/depth, drop-size distribution, drop-velocity distribution and precipitation type are compared from six in-situ precipitation sensor designs over 12 months to assess their performance and provide a benchmark for future design and deployment. The designs considered are: tipping-bucket (TBR), drop-counting (RAL), acoustic (JWD), optical (LPM), single-angle visiometer with capacitor (PWD21) and dual-angle visiometer (PWS100). Precipitation rates are compared for multiple time resolutions over the study period, while drop size and velocity distributions are compared with cases at stable precipitation rates. To examine precipitation type a new index and a logic algorithm to amalgamate consecutive precipitation type observations consistently is introduced and applied. Overall the choice of instrument for deployment depends on the usage. For fast response (less than 15 minutes), the PWD21 and TBR should not be used. As precipitation rate or the duration of a sample increases, the correlation of the TBR with the majority of other instruments increases. However, the PWD21 consistently underestimates precipitation. The RAL,PWS100 andJWDare within ± 15% for precipitation depth over 12 months. All instruments are inconsistent in their ability to observe drop size and velocity distributions for differing precipitation rates. There is low agreement between the instruments for precipitation type estimation. The PWD21 and PWS100 rarely report some precipitation types, but the LPM reports more broadly. Meteorological stations should use several instrument designs for redundancy and to more accurately capture precipitation characteristics.

Influence of Drop Velocity and Droplet Spacing on the Equilibrium Saturation Level in Binder Jetting

Understanding the equilibrium saturation level is crucial to Binder Jetting (BJ). Saturation level influences dimensional accuracy, print time, green strength, and final material properties. Improved understanding of the saturation level can reduce development time for new materials and improve existing processes in BJ. Attempts have been made to predict saturation levels of parts with simple calculations from droplet primitives and capillary pressure. There is, however, limited experimental validation for these methods and they do not include the impact of drop velocity and droplet spacing. This study incorporates the influences of drop velocity and droplet spacing on the saturation level of the part. Drop primitives of varying droplet velocity and droplet spacing were compared. Results show that velocity impacts the feasible parameter space.

Study on Mechanical Properties of Submunition’s Ribbon Straightening Section

The humanitarian damage caused by the unexploded submunitions is one of the hot issues of concern to the international community at present. A portion of the submunition that did not explode was caused by a break at the connection between the ribbon riveting and the fuze. According to the physical structure of the submunition and the trajectory into which it was ejected, we analyzed the forces of the submunition in flight, deduced the related mathematical models, and clarify the key elements of the mechanics. In this paper, the commercial simulation software was used to calculate the mechanical properties of the ribbon. And the variation regularity between drop velocity and straightening force of ribbon are revealed. And the response characteristics of different material ribbon with different sizes of riveting holes and riveting joints under tensile action were simulated. The simulation results show that, in the trajectory environment with 30 m/s~55 m/s typical stream speed, the tensile force of the ribbon is less than 300 N, and the application concentration of the connecting parts of the riveting joint and the ribbon will not cause the failure of the kevlar ribbon, but it will cause the failure of the nylon ribbon. In order to verify the variation of the tension of kevlar ribbons in different trajectory environments, we designed the experimental scheme of tension test of the ribbon straightening section of submunition and conducted experiments. Experimental results and numerical simulation results revealed the same law. This paper provides effective technical support for solving the problem of unexploded submunitions.

Drop mobility on superhydrophobic microstructured surfaces with wettability contrasts

Influence of wettability contrasts and contact angle hysteresis on drop velocity and surface energy analysis describing the drop motion.

Uniform electric-field-induced lateral migration of a sedimenting drop

We investigate the motion of a sedimenting drop in the presence of an electric field in an arbitrary direction, otherwise uniform, in the limit of small interface deformation and low-surface-charge convection. We analytically solve the electric potential in and around the leaky dielectric drop, and solve for the Stokesian velocity and pressure fields. We obtain the correction in drop velocity due to shape deformation and surface-charge convection considering small capillary number and small electric Reynolds number which signifies the importance of charge convection at the drop surface. We show that tilt angle, which quantifies the angle of inclination of the applied electric field with respect to the direction of gravity, has a significant effect on the magnitude and direction of the drop velocity. When the electric field is tilted with respect to the direction of gravity, we obtain a non-intuitive lateral motion of the drop in addition to the buoyancy-driven sedimentation. Both the charge convection and shape deformation yield this lateral migration of the drop. Our analysis indicates that depending on the magnitude of the tilt angle, conductivity and permittivity ratios, the direction of the sedimenting drop can be controlled effectively. Our experimental investigation further confirms the presence of lateral migration of the drop in the presence of a tilted electric field, which is in support of the essential findings from the analytical formalism.

An Experimental Investigation of the Primary Atomization of Viscoelastic Impinging Jets

The primary atomization of a viscoelastic liquid was experimentally investigated using a water-based solution of 0.1 wt.-% xanthan gum (XG). Shadowgraphy images were obtained to qualitatively study the impinging jet spray formation and Phase Doppler Anemometry (PDA) was used to measure the drop diameters and drop velocities. The viscoelastic behavior was observed to hinder atomization when the effect of the inertial force was relatively insignificant. However, increasing the inertial force led to the spray patterns transitioning towards the ligament structures and fully developed patterns. D10, D32, and MMD drop diameters were observed to decrease with increasing inertial force and were larger than mean diameters of a water spray at similar conditions. The mean axial drop velocity was observed to increase with increasing inertial force.