Generation of Concentration Gradients by a Outer-Circumference-Driven On-Chip Mixer

The concentration control of reagents is an important factor in microfluidic devices for cell cultivation and chemical mixing, but it is difficult to realize owing to the characteristics of microfluidic devices. We developed a microfluidic device that can generate concentration gradients among multiple main chambers. Multiple main chambers are connected in parallel to the body channel via the neck channel. The main chamber is subjected to a volume change through a driving chamber that surrounds the main chamber, and agitation is performed on the basis of the inequality of flow caused by expansion or contraction. The neck channel is connected tangentially to the main chamber. When the main chamber expands or contracts, the flow in the main chamber is unequal, and a net vortex is generated. The liquid moving back and forth in the neck channel gradually absorbs the liquid in the body channel into the main chamber. As the concentration in the main chamber changes depending on the pressure applied to the driving chamber, we generated a concentration gradient by arranging chambers along the pressure gradient. This allowed for us to create an environment with different concentrations on a single microchip, which is expected to improve observation efficiency and save space.

PROSPECTS OF APPLICATION OF LIQUID-MOVING SELF-CURING MIXTURES IN THE PRODUCTION OF THIN-WALLED STEEL CASTINGS

The method of manufacturing casting molds and cores for steel and iron casting from liquid self-hardening mixtures has been known since the 60s of the last century. The idea of the method is very simple - after preparation, the LSS is poured into the working cavity of the core box or onto the model installed in the flask, and then it is kept for some time until the foam falls, the core or shape hardens and the gas permeability is restored to operating values. Nevertheless, the method is not widely used in existing production due to a number of disadvantages. The aim of the work is to «revive» it, taking into account modern risks and challenges. Based on the results of the information and analytical review, a critical assessment was made. The directions of improvement and prospects of its use in innovative technology for the production of thin-walled steel casting for critical purposes are determined.

New symmetries, group-invariant solutions, linear differential constraints of a generalized Burgers-KdV equation and its reduction

All we know that the Burgers-KdV equation is extensively used to study the liquid flow with bubbles and the liquid moving flow in the elastic pipes. In this paper, we obtain the Lie point symmetries, self-nonlinear adjointness of a generalized Burgers-KdV equation (GB-KdVE) are obtained, it follows that the conservation laws are worked out. As a reduction of the GB-KdVE, a Burgers equation with general coefficients is presented, whose new strong symmetry and new nonlocal symmetries are generated, respectively. Furthermore, the noninvariant solutions of the GB-KdVE are produced as well. Finally, we propose the double linear differential constraints for GB-KdVE-type so that some soliton solutions are singled out.

Формирование и деформация капель жидкости в микроканалах

An experimental study of drop formation in narrow horizontal microchannels with rectangular cross section and a height from 50 to 150 micrometers was performed. It is shown that in these channels there is a new flow regime when drops moving along the microchannel, which are vertical liquid bridges. Three mechanisms of the formation of such drops are distinguished: the formation directly near the liquid nozzle, the separation of droplets from the liquid moving along the side walls of the channel, and due to the destruction of strongly deformed drops and horizontal liquid bridges. It was found that the deformation of drops increases with an increase in the Weber number. It is shown that when the first critical value of the Weber number is reached, the drops begin to deform, and when the second Weber number is reached, they break.

Liquid Characteristics Under Melting/Solidification Conditions Using Energy Conserving Dissipative Particle Dynamics

In this paper, energy conserving Dissipative Particle Dynamics (DPDe) is used to study liquid characteristics when the walls are kept at a melting temperature. The formulation of the phase change problem is based on the latent heat model available in the literature. It is incorporated into the DPDe method to simulate a one-dimensional solid-liquid moving boundary problem. The solution domain is considered to be a two-dimensional Cartesian box where DPDe particles are randomly distributed. Periodic boundary conditions are applied in the flow direction and solid DPDe particles are placed as additional layers on the top and bottom of the domain. The DPDe result was compared with the available analytical solution and the effects of the DPDe parameters and thermal characteristics are discussed.