Simulation and Experimental Research on the Liquid Spreading Behavior in the Wire Sawn Kerf

The significance of liquid for abrasive wire sawing has been demonstrated by researchers with considerable studies. However, its performance in the spreading behavior is limited by the development trend of larger area wafer and narrower slicing kerf. Nevertheless, studies on the liquid spreading behavior in the wire sawing kerf are awfully limited. In this paper, a 3D CFD (Computational Fluid Dynamics) model was presented to simulate the liquid spreading behavior in the kerf. Where a VOF (Volume of Fluid) method with a CSF (Continuum Surface Force) model is used to simulate multiphase flow, and an empirical correlation for characterizing the liquid dynamic contact angle is introduced using UDF (User Defined Functions). Parametric simulations were performed on the kerf area, kerf width, liquid viscosity, liquid surface tension and liquid velocity at the inlet area of the kerf. Verification experiments are conducted for the validity of the simulation model. From both simulation and experimental results, three typical liquid spreading regimes in the kerfs are found, which perform distinct different effects on wire sawing. Moreover, the limiting conditions of the three spreading regimes are identified by non-dimensional analysis, then a prediction model is proposed for the liquid spreading regime, by given a set of Weber number and Capillary number. For wire sawing, the increase in the wafer area will not change the liquid spreading regime in the kerf, but the reduction of the kerf width will significantly hinder the liquid spreading behavior. By adjusting the physical properties and supply conditions of the liquid, the spreading regime can be effectively converted to facilitate wire sawing.

Surface-Tension-Confined Channel with Biomimetic Microstructures for Unidirectional Liquid Spreading

Unidirectional liquid spreading without energy input is of significant interest for the broad applications in diverse fields such as water harvesting, drop transfer, oil–water separation and microfluidic devices. However, the controllability of liquid motion and the simplification of manufacturing process remain challenges. Inspired by the peristome of Nepenthes alata, a surface-tension-confined (STC) channel with biomimetic microcavities was fabricated facilely through UV exposure photolithography and partial plasma treatment. Perfect asymmetric liquid spreading was achieved by combination of microcavities and hydrophobic boundary, and the stability of pinning effect was demonstrated. The influences of structural features of microcavities on both liquid spreading and liquid pinning were investigated and the underlying mechanism was revealed. We also demonstrated the spontaneous unidirectional transport of liquid in 3D space and on tilting slope. In addition, through changing pits arrangement and wettability pattern, complex liquid motion paths and microreactors were realized. This work will open a new way for liquid manipulation and lab-on-chip applications.

Determination of flood parameters during the fire hazardous liquid spreading after the accident

Пролив пожароопасных жидкостей на свободную поверхность является одним из наиболее опасных сценариев аварии, приводящей к пожару. Для решения задачи по оценке параметров такого пролива было использовано численное интегрирование уравнений сохранения методом Годунова, на примере растекания пожароопасной жидкости по бетонному основанию. Возможности метода численного интегрирования позволяют спрогнозировать размеры пролива на текущий момент времени. Результаты расчета показали, что пролив объемом 245 м в течение 4-5 мин достигает равновесного состояния, после чего площадь зеркала пролива практически не увеличивается. Nowadays, various containers are used for storage and transportation of fire hazardous liquids. It is impossible to eliminate completely the possibility of tank depressurization and the scenarios associated with their destruction should be taken into account when developing technical solutions and organizational measures aimed at minimizing the possible consequences of such accidents. As a result of the flammable liquid spreading a mirror of the flood can form, from which subsequently the evaporation of combustible products occurs, which, when mixed with air, forms explosive mixtures. At a fuel concentration in the cloud above the upper limit of flame propagation, a fire development characterized by a flash fire is possible. If the concentration of vapors in the mixture with air is inside the concentration region of the flame propagation, a deflagration explosion is possible. In both cases, a flood fire can occur characterized by the formation of a high temperature flame. The initial task in predicting such accidents is to determine the surface area of the spilled liquid from which evaporation can occur. To solve this problem it is necessary to solve the hydraulic problem associated with the fluid spreading on a free surface having hydraulic resistance. Similar problems were solved in the practice of building design while determining the parameters of water movement along a dry riverbed. One of the forms of solution is the method of numerical integration of the conservation equations with the Godunov method, which is effective in solving problems of gas dynamics, as well as hydraulic problems. The calculation results showed that this method is applicable to the considered problem of forming a fire hazardous liquid flood on a free surface. Also, the results of the work indicate that a very significant volume of the fire hazardous liquid flood (245 m) reaches quickly enough a quasi-equilibrium state with a flood thickness of 0.03 ч 0.04 m.

Enhanced Pool Boiling Heat Transfer During Quenching on Micro/Nanostructured Wicking Surface: Effects of Submicron-Scale Substructures

Micro/nanostructured wicking surfaces with different submicron-scale substructures were fabricated by using electrochemical deposition and chemical etching methods on stainless steel spheres. Quenching experiments were carried out on these surfaces in saturated water to reveal the effect of submicron-scale substructures on the boiling heat transfer enhanced by wickability. The results indicated that, as compared to the knife-like submicron-scale substructure, the needle-like substructure improved the wickability of wicking surface, but has a weaker boiling heat transfer enhancement. The difference in wicking/spreading performance between two wicking surfaces with different submicron-scale substructures could not be enough to significantly affect the boiling heat transfer during quenching. However, the knife-like substructure might have a larger specific surface area, resulting in a greater boiling heat transfer enhancement. Besides, liquid spreading distance measured at room temperature might not be suitable for the wickability characterization.