Experimental investigation of viscous effects upon a breakup of droplets in high-speed air flow

The deformation and disintegration of water and silicone oil droplets were investigated experimentally in a shock tube. Optical visualization was performed by means of the shadowgraph method. Droplets with diameters in the range of 200 to 500 m were generated by an oscillating capillary. The smallest Weber number in the present experiments is close to the critical value of the breakup. The droplets disintegrated in the stamen or bag mode for moderate values of the Weber number. The effect of the viscosity of the liquid on the breakup mode and the breakup time is discussed.     

Viscoplastic dynamics of isotropic plates of variable thickness under explosive loading

A problem of viscoplastic dynamic bending of isotropic plates of variable thickness is formulated. A method for integrating the initial-boundary problem is developed. Numerical results are compared with a known analytical solution obtained within a rigid-plastic model; good agreement is demonstrated. The efficiency of the method developed is verified by numerical computations. It is shown that the final flexure of plates can be reduced severalfold by applying rational design. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 2, pp. 123–134, March–April, 2007.     

Collision and merging of two equal droplets of propanol

Equally spaced and uniform droplets are produced by a vibrating orifice and move away in a straight line. They intersect with an exactly equal string of droplets and collide one by one. With stroboscopic lighting and multiple exposures, they are photographed. Thus successive stages of the collision process are shown on a single photo. The droplets can be made to collide with or without angular momentum by adjusting the aim of the emitting orifices. The impacting speeds can be varied from 2.8 to 11.7 m/s. Droplet sizes from 70 to 200 m are employed. Motions of the coalesced drop after the merging are bizarre and well-displayed. The results are important for spray modeling. When the streams of droplets merge at higher speeds, they may distort to the extent that the two streams of droplets merge to a single continuous sinuous stream.List of symbols b collision parameter - d diameter - p pressure difference - f frequency - u impact velocity - v droplet velocity - V liquid feed rate - x, y, z rectangular coordinates - angle between droplet stream and symmetry line - G generator - i initial, before the collision - P particle - T droplet - 1, 2 first and second droplet generator     

Binary collision dynamics of fuel droplets

An experimental study has been carried out in which the collision dynamics of two n-haxane fuel droplets are studied. The experiments are performed on the collision of two burning droplets, as well as two nonburning droplets, to assess the influence of the high temperature combustion environment on the dynamics of the collision.The results indicate that as the Weber number is increased, the collision type moves toward higher energy collision, and for the same Weber number, different types of collisions, depending on the local value of the collision impact parameter, may occur. In the range of the Weber numbers studied, the results show that for the nonburning droplets, the collision type can be bouncing, grazing, temporary coalescence-satellite generating, or permanent coalescence, depending on the local value of the impact parameter. For the burning droplets in the same initial Weber number range, only temporary coalescence and permanent coalescence are observed.     

Interaction phenomena between liquid droplets and hot particles—Captured via high-speed camera

The interaction of evaporating droplets and hot catalyst particles plays a major role in heterogeneously catalysed reactions.The liquid feed is injected into a gas–solid flow and is mixed with the catalyst.The interaction phenomena determine the evaporation time which should be minimised to keep the reactor vessel small.First measurements with a bed of fixed hot FCC-particles(fluid catalytic cracking)and two model fluids have been conducted.The interactions of ethanol and water droplets with the hot bed sur...     

Dependence of combustion dynamics in a gasoline engine upon the in-cylinder flow field, determined by high-speed PIV

We apply time-resolved high-speed particle image velocimetry (PIV) in an optically accessible gasoline engine to determine the effect of the in-cylinder flow field upon combustion dynamics. Our PIV setup involves solid particles as tracer, which enables also measurements at firing top dead center and during the combustion process itself. We analyze the flow field for the entire intake and compression phase, as well as the decay of a prominent large-scale tumble structure in the flow field. The data indicate significant cycle-to-cycle flow field variations, characterized by detection of kinetic energy and tumble center. Measurements in fired engine operation demonstrate the influence of the flow field on combustion dynamics. At stoichiometric operation, we find that variations in the kinetic energy of the flow field are a major cause of cycle-to-cycle variations. From simultaneous imaging of the combustion flame and PIV at lean operation, we find that the velocity distribution in the flow field induces a macroscopic motion of the flame kernel??which significantly effects the combustion process.     

Vibrational equations of variable mass layers and membranes

Vibrations of layers and membranes, consisting of variable mass particles [1, 2], are considered. Adjacent and separated particles are classified. Differential equations and natural boundary conditions of vibrations of variable mass layers and membranes are derived. Two examples for vibrations are integrated by means of separation of variables.Translated from Zhurnal Prikladnoi Mekbaniki i Tekhnicheskoi Fiziki, No. 5, pp. 138–143, September–October, 1973.     

Axisymmetric spherical shell with variable wall thickness

This paper is engaged in research of the problem of axisymmetric spherical shell with variable wall thickness. The solutions for the problem are given for the spherical shell segment which does not contain the pole of sphere and the point of zero wall thickness. First Received July 24, 1982     

Collision between high and low viscosity droplets: Direct Numerical Simulations and experiments

Binary droplet collisions are of importance in a variety of practical applications comprising dispersed two-phase flows. In the present work we focus on the collision of miscible droplets, where one droplet is composed of a high viscous liquid and the other one is of lower viscosity. This kind of collisions take place in, for instance, spray drying processes when droplets with different solid content collide in recirculation zones. The aim of this paper is to investigate the details of the flow inside the colliding droplets. For this purpose, two prototype cases are considered, namely the collision of equal sized droplets and the collision between a small and highly viscous droplet and a bigger low viscous droplet. A new experimental method has been developed in order to visualize the penetration and mixing process of two colliding droplets, where a fluorescence marker is added to one liquid and the droplets are excited by a laser. The results show a delay in the coalescence which takes place during the initial stage of a collision of droplets with different viscosities. Direct Numerical Simulations based on the Volume-of-Fluid method are used to study these collisions and to allow for a more detailed inspection of the mixing process. The method is extended to consider a second liquid with a different viscosity. In order to reproduce the delay of coalescence, an algorithm for the temporal suppression of the coalescence is applied. A predictive simulation of the delay is not possible, because the extremely thin air gap separating the droplets cannot be resolved by the numerics. This approach is validated by comparison with experimental data. The results provide local field data of the flow inside the collision complex, showing in particular a pressure jump at the liquid–liquid interface although no surface tension is present. The detailed analysis of the terms in the momentum balance show that the pressure jump results from the viscosity jump at the liquid–liquid interface.