Thin Laminar Flow Research Articles

Scanning process of micro-spark assisted chemical engraving (SACE) based on thin laminar flow electrolytes and given narrow machining gaps

Spark assisted chemical engraving (SACE) has the advantages of less contact stress and little/no tool electrode wear, and it is expected to achieve damage-free processing on dielectric workpieces. The key factors of electrolyte depths and machining gaps play an important role in the SACE process, especially for a micro-SACE process. Currently, there is still no convenient method for forming a thin and stable electrolyte depth in a scanning process of micro-SACE, and the existing methods are difficult to specify a micron-level machining gap between a tool electrode and a workpiece. In order to solve these problems, a scanning process of micro-SACE based on the thin laminar flow electrolyte and the narrow machining gap was proposed. This research focuses on the experiments to obtain the controllable rules of a stable thin film of electrolyte for concentrating the processing energy and restricting the processing locality. A novel method of indirect electric contact was presented for measuring workpiece surface height and then precisely leveling the workpiece surface before the scanning process. A micro-feed contact method with CCD (charge coupled device) vision was used to give a narrow machining gap. In experiments, the leveling accuracy of workpiece surface can reach ± 0.1 μm/mm, and the adjusting resolution of micro-machining gaps can be down to a precise scale of ± 0.5 μm. As a result, a micro-structure of 1.2 × 1.2 mm with a depth removal resolution down to ~ 2 μm was achieved on the surface of ZrO2 workpiece with the flow layer electrolyte as thin as 165 ± 5 μm.

Laser-induced breakdown spectroscopy assisted by machine learning for olive oils classification: The effect of the experimental parameters

Laser Induced Breakdown Spectroscopy (LIBS) was combined with some machine learning techniques, such as Principal Components Analysis (PCA) and Linear Discriminant Analysis (LDA) in order to obtain useful information concerning the classification of olive oil samples (authentication of their geographic origin) and the detection of adulteration. Since the plasma characteristics can depend substantially on the state of a sample (solid, gas or liquid) three different configurations of handling the sample were examined, spray of olive oil, a thin laminar flow and the free surface of few gr of olive oil sample. Then, the effects of experimental parameters, such as the laser energy, the temporal gating conditions (i.e., delay time and integration time) of the CCD detector of the spectrometer, on the plasma characteristics and subsequently on the classification results, were thoroughly investigated and analyzed. The combination of LIBS with the machine learning techniques used, resulted in excellent classification results of the olive oils studied, achieving classification accuracies of 100%.

Measurements and predictions of thermophoretic soot deposition

A thin laminar flow channel with a transverse temperature gradient was used to examine thermophoretic deposition of soot aerosol particles in experiments and modeled in Fire Dynamics Simulator (FDS) simulations. Conditions investigated included three flowrates, with nominal Reynolds number based on the hydraulic diameter of 55, 115 and 230, and two applied temperature gradients, nominally 10 °C/mm and 20 °C/mm, with repeats. Soot was generated from a propene diffusion flame. The burner exhaust was mixed with dilution air, and most large agglomerates greater than 1 μm aerodynamic diameter were removed prior to the channel inlet. The expected thermophoretic velocity of the aerosol was calculated from the applied temperature gradient. A calculated deposition velocity was determined from the mass of deposition, the channel inlet soot concentration, and the exposure time. Uniform soot deposition allowed targets to be used to measure the mass of deposition on the cold side of the channel. The mass of deposition was also determined by subtracting the mass of soot exiting the channel from the mass of soot entering the channel during the exposure time. The deposition velocities from these two methods generally agreed with the thermophoretic velocity and with each other. The deposition mass predicted by the FDS model also compared well with the experiments in most cases. The disagreements for the lowest flow rate cases are attributed to buoyant flow effects adding uncertainty to the actual temperature gradients present in the channel. (The opinions, findings, and conclusions expressed in this paper are the authors’ and do not represent the views or policies of NIST or the United States Government.)

Fine Particle Monolayers Made by a Mobile Dynamic Thin Laminar Flow (DTLF) Device

This paper presents an innovative device for monolayer preparation that takes full advantage of the dynamic thin laminar flow method (DTLF). The small cylinder system provided the opportunity to prepare monolayers continuously and transfer them onto a solid substrate while moving. Hydrophilic and hydrophobic surfaces were coated with fine polystyrene particles. Multilayers were also made by simply moving the mobile DTLF device back and forth over the same surface. Technically, this was achieved by controlling the cylinder rotation and translation speeds above the substrate with a set of electrical motors. The injection of various suspensions into the thin liquid film was performed with syringes to make the fluids emerge near the rotating glass surface. The whole assembly was mounted on a mobile platform. Three fine latex particles were selected to make the primary tests of the new DTLF device. In all cases mono- and multilayers were obtained. This device opens a new avenue for the deposition of monolayer strips onto m2 large surfaces.

Fine Particle 2D Crystals Prepared by the Dynamic Thin Laminar Flow Method

A novel method to make 2D crystals of fine particles is proposed. It is based on the hydrodynamic properties of thin laminar flow. To explore the possibilities of this method, we chose two variables, the particle diameter and the surface charge density. The spherule diameter varied from 6 μm to 53 nm, and its calculated surface charge density from 1134 to 4 μC/cm2. In every case, we easily obtained a rate of monolayer preparation up to 1 mm/s. Moreover, 2D crystals were always observed. The subphase ionic condition was the key parameter providing an adsorption window wide enough to allow a controlled particle−air/water interface adsorption, while maintaining particle−particle repelling electrostatic forces strong enough to avoid fractal formation during the surface compression. This report demonstrates that the DTLF method is an efficient way of producing monolayers and 2D crystals of colloids and that it could be developed to work in a continuous mode.

Dynamic Thin Laminar Flow Method for Making Protein Monolayers

This paper describes a new way to make protein monolayers rapidly. This process reduces the protein contact time at the air−water interface, which subsequently prevents structural alteration. High-speed protein monolayer preparations are obtained by confining proteins in a thin laminar flow liquid film at various speeds. A prototype made of a rotating glass cylinder compressing cytochrome P450scc validated this method. The cytochrome P450 monolayers were verified by optical microscopy, TEM, STM, and AFM. Possible protein 1D crystallites were observed. A rate of protein monolayer preparation up to 2 cm/s was easily obtained. This method is suitable for continuous protein monolayer production and fine particle coating.

Turbulent flow in capillary gas chromatography—evaluation of a theoretical concept by Golay

Early in 1989, the late Marcel Golay derived a theory for turbulent flow capillary gas chromatography. He assumed that the flow pattern under turbulent conditions consists of a turbulent core separated from the tube wall by a very thin laminar flow layer. Further, it was assumed that the viscosity and the diffusion constant are uniform within the turbulent core. The core radius is a fraction p of the tube radius; the core viscosity is m times the laminar flow viscosity and the core diffusivity is assumed to be d times the laminar flow diffusion constant. Values for p, m and d have to be calculated from experimental data; p, m and d are essentially functions of Reynolds number ( Re). Using experimental data obtained in the laboratory, Golay's plate-height theory was evaluated for turbulent flow gas chromatography. In this verification an empirical relationship was used for the average turbulent diffusion constant as a function of Reynolds number and an empirical relationship for the thickness of the laminar sublayer. Further, it was assumed that m = d (Reynolds' analogy). The experiments and theory agree fairly well at Re = 6200; at lower and higher values of Re the agreement is much poorer. The disagreement may be due to the empirical relationships used or to the postulations in the theory: Golay assumed a discontinuous change from laminar to turbulent viscosity and diffusion constants. In engineering literature often a gradual change in properties from the laminar sublayer to the turbelent and in the turbulent core is assumed.

Formation of Roll-Waves on Thin Laminar Flow down an Inclined Plane Wall

The linear stability of periodic permanent roll-wave trains on thin laminar flow of a viscous fluid down an inclined plane wall has been investigated analytically on the basis of a hydraulic model. The analytical result is here confirmed by following numerically the time development of a periodic initial disturbance superimposed upon a basic steady parallel flow into a stable or unstable permanent roll-wave train. Furthermore, it is shown that roll-waves can be generated successively from a localized initial disturbance.

Stability of Roll-Waves on Thin Laminar Flow down an Inclined Plane Wall

This paper considers the roll-wave phenomenon on thin laminar viscous flow down an inclined plane wall on the basis of hydraulic equations which are derived on the assumptions of long wave and parabolic velocity profile. Wave fronts are approximated by discontinuous jumps satisfying physical laws. The solution for the permanent roll-wave train obtained involves one free parameter, and is insufficient to explain observed results. Then, the stability of the said solution to infinitesimal disturbances is investigated. It is found that the roll-wave train is unstable if its wave length is shorter than a certain critical value. Furthermore, wave lengths of the most stable waves are favourably compared with those of waves observed in experiments.