Flow Micro Research Articles

Study on turbulence control method and surface quality analysis of softness abrasive flow machining

To improve mould structural surface quality, the softness abrasive flow (SAF) finishing method is proposed. By setting restrained component to the mould surface, restrained flow passage can be set up. In the flow passage, micro force and quantity cutting for the tiny scale structural surface is realised by using the turbulence wall effect of SAF. Dynamical model of SAF is established based on liquid-solid two-phase flow coupling theory. Semi-annular flow passage is taken as the research object, and turbulent parameters with different flow passages are analysed by using standard k-e turbulent model and discrete phase model (DPM), which is used for describing the influence to turbulent state caused by different boundary conditions, meanwhile, the optimisation design of finishing parameters can be obtained. Finishing platform is constructed, and finishing experiment results show that with the SAF method, the roughness machined is less than Ra 62 nm.

Regimes of two-phase flow in micro- and minichannels (review)

The review deals with the analysis of the factors affecting the boundaries of two-phase regimes in the channels of different cross sections, whose minimal size is less than the capillary constant. The channels are classified by size. Data for two-phase flow regimes are systematized and summarized in tables for the round and rectangular tubes. It is indicated that the most studies identify the following two-phase flow regimes: bubble, slug and annular. The regimes found in some papers are described. The terminology used to describe the regimes is kept. Here we analyze the main factors affecting the structure of the two-phase flow, such as gas and liquid flow rates, parameters of the channel and input section, wettability of the inner surface of channels, liquid properties, and gravitational forces. It is shown that development of instability of the two-phase flow has a significant impact on formation, evolution, and change of the flow regimes.

STEAL 03Н18К9М5Т-ЭЛ THERMIC TREATMENT IMPACT ON MICROFLOW AND REPEATED DEFORMATION PARAMETERS

The paper addresses parameter correlation of microfl ow process with fatigue resistance results. The research has been performed on steel 03Н18К9М5Т-ЭЛ (ВСК-210). The mentioned steel has been subjected to hardening with further drawing at various temperatures.

Differentiation of Atypical Hepatocellular Carcinoma from Focal Nodular Hyperplasia: Diagnostic Performance of Contrast-enhanced US and Microflow Imaging

To evaluate diagnostic performance of contrast-enhanced (CE) ultrasonography (US) and microflow (MF) imaging in differentiation of atypical hepatocellular carcinoma (HCC) from focal nodular hyperplasia (FNH). Institutional review board approval was obtained, and informed consent was waived. A total of 103 patients (mean age, 43.9 years; age range, 17-75 years) were included; 38 patients with HCC and 65 with FNH underwent CE US, and vascular architecture pattern (VAP) and arrival time parametric (ATP) images were analyzed. Resident and staff radiologists independently and retrospectively reviewed CE US, VAP, and ATP images. χ(2) test and logistic regression analysis were applied to identify specific features of FNH or HCC on CE US and MF images. To compare diagnostic performance of CE US with or without MF imaging, four sets of criteria were assigned: (a) routine CE US alone, (b) VAP and CE US, (c) ATP imaging and CE US, and (d) all three methods in combination. Sensitivity, specificity, accuracy, and area under the receiver operating characteristic curve (AUC) of resident and staff radiologists were analyzed. Cohen κ statistic was used to assess agreement of CE US and MF imaging features between staff and resident radiologists. MF imaging offered significant improvements over most detection rates achieved with routine CE US signs in both groups. For staff radiologists, AUCs from criteria sets 3 (AUC = 0.873, P < .05) and 4 (AUC = 0.887, P < .05) were significantly higher than AUC from criteria set 1 (AUC = 0.835). For resident radiologists, specificity (71% and 69% vs 25%, P < .01) and accuracy (78% and 79% vs 50%, P < .01) of criteria sets 3 and 4 were significantly higher than those of criteria set 1. Moreover, AUCs for criteria sets 2 (AUC = 0.728, P < .05), 3 (AUC = 0.823, P < .01), and 4 (AUC = 0.857, P < .01) were significantly higher than those for criteria set 1 (AUC = 0.667). When compared with routine CE US, MF imaging can more effectively depict specific features and offers improved diagnostic performance in the differentiation of atypical HCC from FNH, especially when used by resident radiologists. Online supplemental material is available for this article.

Process intensification of copper chromite (CuCr2O4) nanoparticle production using continuous flow microreactor

The present study deals with the production of monodispersed copper chromite nanoparticles in a continuous flow micro channel reactor. The precursors used were aqueous solutions of copper nitrate and chromium nitrate. A mixture of the precursor at a fixed copper to chromium metal ion ratio and citric acid were infused in a continuous flow microreactor maintained at a constant temperature of 80°C and followed by calcinations at 200°C for a fixed duration of 2h to yield the nano powder. The effect of different Cu/Cr metal ion ratios on the particle size was studied. The optimum value of flow rate and Cu/Cr ratio was found to be 75 and 0.5mL/h, respectively. The particle size of obtained copper chromite nanoparticles was measured to be in the range 192–300nm, relatively smaller compared to that obtained in a batch reactor. The effect of different types of surfactants on the particle size was also studied and it was observed that the surfactants played an important role in controlling nucleation during particle formation and subsequent growth of the particles.

Modeling the Energy Extraction from In-stream Water by Multi Stage Blade System of Cross Flow Micro Hydro Turbine

This paper aims to present energy extraction behavior of multi stage Micro Hydro Turbine (MHT), particularly when it operates in a low velocity In-Stream water body. Development a MHT with multi stage blade (runner) for water velocity ranges from 0.5m/s to 1.0m/s is the novelty of this research. Findings of literature review on MHT and simulation results of ANSYS CFD software are the basis of designing this research project. The vital parameters involved in designing the turbine were blade area, blade stage, blades position against water flow direction, spacing between blades, blade materials; and other technical factors associated with turbine operations. The study revealed that the turbine had started to extract energy at water velocity 0.3m/s at 35 RPM turbine speed. At water inlet velocity 1.1m/s, the velocity drop across blade was 25.6% and the energy extraction efficiency was 48.3%. The findings demonstrated that the energy extraction capacity of turbine blade had been greatly influenced by the blade stages and water velocity. The study concludes that the developed turbine is useful in low velocity In-stream water body for energy extraction and would be able to contribute to achieve energy and environmental sustainability.

フロー·マイクロ合成技術のメディシナルケミストリーへの展開

フロー·マイクロ合成技術のメディシナルケミストリーへの展開

Research of Bidirectional Power Flow Algorithm of Micro-Grid Based on the Improved Zbus Method

Themicro-grid technology is an effective way to promote renewable energydevelopment and utilization. Low voltage micro-grid can absorb photovoltaic,wind power and other large number of scattered random distributed power supply,and the system may be three-phase asymmetry while operation, randomness of thepower output and load is stronger. Therefore an improved bidirectional power flow algorithm is putforward suitable for low voltage micro-grid. According to the physicalstructure components of the micro-grid and different kinds of micro powersupply, the types of micro-grid in power flow calculation is studied to dealwith complex node in the micro-grid, improved Zbus algorithm is proposed tocalculate the power flow of micro -grid .IEEE-69 is taken as an example for simulation, the resultsshow that the proposed method is better for the biggest error ratio of voltagedrop and calculation time than traditional method. Atthe same time the algorithm is also suitable for island operation state of the microgrid.

Experimental investigation of two-phase slug flow splitting at a micro impacting T-junction

As a fluid distribution unit, the micro T-junction is commonly found in various devices, such as micro-reactors and compact heat exchangers. It is well known that phase split occurs during gas–liquid two-phase flow through T-junction and causes different qualities between the branches of the tee, which can have a significant influence on the performance of equipments downstream. This paper presented the results of an experimental investigation conducted on phase split of slug flow through a horizontal T-junction with a square cross section (500μm×500μm). Nitrogen and water at room temperature of 18°C were used as the test fluids. The inlet superficial velocity ranges of gas and liquid were 0.36–2.4m/s and 0.1–0.9m/s, respectively. The aqueous solutions of sodium dodecyl sulfate (SDS) with different mass concentrations were used to study the effect of surface tension. Experimental results showed that, decreasing the channel diameter drastically intensified the phase maldistribution due to the effect of surface tension. In particular, for the micro impacting T-junction, once the liquid taken off from either branch was smaller than 35%, there was no gas taken off. Besides, the effect of surface tension took on distinct characteristics under different inlet flow conditions. Specifically, for the short gas slugs, the phase maldistribution reduced with decreasing surface tension. However, for the long gas slugs, the phase maldistribution got worse with the decrease of surface tension. Finally, a correlation capable of predicting the phase split of slug flow in micro impacting T-junctions was developed.

Modeling of thermodynamic properties of an oxygenate + aromatic hydrocarbon: Excess molar enthalpy

Excess molar enthalpy (HmE) have been measured at 303.15K for 1-propanol+benzene or toluene or o- or m- or p-xylene mixtures using flow micro calorimeter. The HmE versus x1 plots are skewed toward y-axis showing maxima at x1≈0.3. At (x1=0.5) HmE vary in the order: toluene<benzene<m-xylene<p-xylene∼o-xylene. The excess volume data have also been interpreted in terms of Graph-theoretical approach and Prigogine–Flory–Patterson theory. It has been observed that while PFP theory fails to predict the HmE values for these systems in the composition range x1<0.5, agreement with experimental values is reasonably good thereafter. The HmE values calculated by Graph theory compared well with the corresponding experimental values.

Impact on the Performance of Micro-Nozzle Straight Exit Section

The FLUENT6.3 software is applied to simulate the supersonic flow in micro convergent-divergent nozzle. The simulation is complemented by computing steady 2-D Navier-stokes equations to analyze the pressure contour and velocity contour inside the micro nozzle which has straight exit section or not and the length of straight exit section l. Also the performances of fluent mass coefficients and thrust force efficiencies are studied. The numerical results show: That the nozzle has straight exit section or not and the section length l affect the pressure contour and velocity contour inside the thruster. Compared to the nozzle that has no straight exit section, the minimum pressure region and the maximum velocity region are close to the center of exit in the nozzle that has straight exit section. Also the affected region is increased. When the throat Reynolds number Re is small, the flow coefficient Cd and thrust coefficient ηF firstly increase then decrease with the increase of l.

A continuous flow micro filtration device for plasma/blood separation using submicron vertical pillar gap structures

This work demonstrates a continuous flow plasma/blood separator using a vertical submicron pillar gap structure. The working principle of the proposed separator is based on size exclusion of cells through cross-flow filtration, in which only plasma is allowed to pass through submicron vertical pillars located tangential to the main flow path of the blood sample. The maximum filtration efficiency of 99.9% was recorded with a plasma collection rate of 0.67 µl min−1 for an input blood flow rate of 12.5 µl min−1. The hemolysis phenomenon was observed for an input blood flow rate above 30 µl min−1. Based on the experimental results, we can conclude that the proposed device shows potential for the application of on-chip plasma/blood separation as a part of integrated point-of-care (POC) diagnostics systems.

An efficient method for simulation of the dynamics of a large number of deformable droplets in the stokes regime

Direct simulations of the interaction of a large number of deformable droplets are necessary for more accurate predictions of rheological properties and the microstructure of liquid-liquid systems. In the present study, a mathematical model of a three-dimensional flow of a mixture of two Newtonian liquids of a droplet structure in an unbounded domain at low Reynolds numbers is considered. An efficient computational method for simulation of the dynamics of a large number of deformable drops is developed and tested. This approach is based on the boundary element method for three-dimensional problems accelerated both via an advanced scalable algorithm (FMM), and via utilization of a heterogeneous computing architecture (multicore CPUs and graphics processors). This enables direct simulations of systems of tens of thousands of deformable droplets on PCs, which is confirmed by test and demo computations. The developed method can be used for solution of a wide range of problems related to the emulsion flow in micro- and nanoscales. Also it can be used to establish the closing relations for simulation of two-phase liquid-liquid flow based on the continuum approach in macroscales.

Analysis of mixing for electroosmotic flow in micro/nano channels with heterogeneous surface potential

Electroosmotic flow in micro and nano channels deals with the low Reynolds number effects due to weak inertial forces. It requires a very long channel for mixing of different species in low Reynolds number through diffusion. The motivation of the present study is to increase the mixing performance when more than one species with heterogeneous surface potential is considered. The generation of vortical flow due to the presence of wall heterogeneity at different locations of the channel is discussed. The flow characteristics for the present study are obtained by numerical solution of the Poisson equation, the Nernst–Planck equation, and the Navier–Stokes equation, simultaneously. A numerical method based on the pressure correction iterative algorithm (SIMPLE) is adopted to compute the flow field and mole fraction of the ions. The potential patch along the channel walls induces a strong recirculation vortex which in turn generate a strong pressure gradient to increase the mixing performance. The streamlines follow a tortuous path near patches.

Flow Micro‐Calorimetry and FTIR Spectroscopy Study of Interfacial Interactions in Uncoated and Coated Calcium Carbonate Filled Polyurethane Adhesives

SummaryThermoplastic polyurethane (TPU) ‐ calcium carbonate interactions were studied using flow micro‐calorimetry (FMC) and diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS). FMC enabled the determination of adsorption and desorption energies; in this study a model compound approach was used to acquire insight in to the effect of calcium carbonate type and presence of stearate coating on polymer – filler interactions. It was anticipated that this data will assist in the understanding of differing responses obtained from parallel plate rheometry and viscoelastic measurements of the filled polyurethanes. Three calcium carbonates (coated and uncoated precipitated calcium carbonate, and natural ultramicronized uncoated calcium carbonate) were used. A stronger TPU‐filler interaction was shown in the uncoated precipitated calcium carbonate due to the fact that more of the surface was available for interaction.

Effect of surface roughness on liquid friction and transition characteristics in micro- and mini-channels

A general threshold was proposed to subdivide a flow in a smooth or a rough micro- and mini-channel. A database was setup based on the experimental results of liquid flow in rough micro- and mini-channels from the literature, which includes 5569 data and covers wide ranges of the relative roughness and the Reynolds number. The effect of roughness on a flow in micro- and mini-scale channels was investigated by in-depth analyzing the friction factor and the flowing transition characteristics. Existing prediction models were used to predict the friction factors of fully developed flow and critical Reynolds number. Both experimental data and the predictions showed that roughness had little effect on flow characteristics when the relative roughness (ε/Dh) is less than 1%, while for the relative roughness larger than 1%, the friction factor and critical Reynolds number gradually deviate from the prediction values of smooth tubes. It was recommended that ε/Dh = 1% could be set as a threshold to distinguish smooth and rough micro- and mini-channels. According to this criterion, new correlations to predict friction factor and critical Reynolds number were also fitted. Moreover, it was also concluded that geometries of the channels had little effects on this threshold.

A design method for rectangular microchannel counter flow heat exchangers

This paper presents a method for designing rectangular microchannel counter flow heat exchangers. The adopted methodology is based on two models: a one-dimensional model and a CFD model. A one-dimensional model for parallel plate micro heat exchangers is adopted to adjust the geometries of the rectangular microchannel counter flow heat exchanger. To this end a hydro-dynamically and thermally equivalent parallel plate heat exchanger is used. A more accurate CFD model serves to fit the parameters of the one-dimensional model. The related correction factors are presented for a range of pressure drops and axial conduction parameters. The present study provides quantitative data for the optimal plate dimensions and resulting maximal power density of a gas–gas rectangular channel counter flow micro heat exchanger with effectiveness varied between 0.6 and 1.

Coupled lattice Boltzmann method for simulating electrokinetic flows: A localized scheme for the Nernst–Plank model

We present a coupled lattice Boltzmann method (LBM) to solve a set of model equations for electrokinetic flows in micro-/nano-channels. The model consists of the Poisson equation for the electrical potential, the Nernst–Planck equation for the ion concentration, and the Navier–Stokes equation for the flows of the electrolyte solution. In the proposed LBM, the electrochemical migration and the convection of the electrolyte solution contributing to the ion flux are incorporated into the collision operator, which maintains the locality of the algorithm inherent to the original LBM. Furthermore, the Neumann-type boundary condition at the solid/liquid interface is then correctly imposed. In order to validate the present LBM, we consider an electro-osmotic flow in a slit between two charged infinite parallel plates, and the results of LBM computation are compared to the analytical solutions. Good agreement is obtained in the parameter range considered herein, including the case in which the nonlinearity of the Poisson equation due to the large potential variation manifests itself. We also apply the method to a two-dimensional problem of a finite-length microchannel with an entry and an exit. The steady state, as well as the transient behavior, of the electro-osmotic flow induced in the microchannel is investigated. It is shown that, although no external pressure difference is imposed, the presence of the entry and exit results in the occurrence of the local pressure gradient that causes a flow resistance reducing the magnitude of the electro-osmotic flow.

Determining the intrinsic permeability of tight porous media based on bivelocity hydrodynetics

For tight porous media, the permeability measured from the Darcy test is only an apparent permeability because the Klinkenberg effect occurs when the Knudsen number is high. To determine the intrinsic permeability, we need a simple and rigorous permeability correction that is valid in the entire flow regime. Thus, introducing a non-Maxwellian slip boundary condition, we develop the bivelocity hydrodynetics in this paper. The bivelocity hydrodynetics is defined by combining bivelocity hydrodynamics with kinetic theories. In the framework of the bivelocity hydrodynetics, we derive a simple and rigorous permeability correction based on the analytical solutions of rarefied gas flows in micro- and nano-tubes. After compared with conventional solutions and experiments, the present solutions are validated in the entire flow regime. Moreover, the validation is also a clear proof for the bivelocity theories.

Experimental analysis of the influence of wall axial conduction on gas-to-gas micro heat exchanger effectiveness

In this paper an experimental investigation of the thermal performances of gas-to-gas micro heat exchangers operating under different flow configurations (co-current, counter-current, cross flow) is presented and the results are compared with the predictions of the conventional correlations developed for the design of the conventional-sized heat exchangers. A double-layered microchannel heat exchanger has been specifically designed in order to be able to reproduce co-current, counter-current and cross flow gas arrangements. The core is housed in a shell made of polymer; on the contrary, the foil between the hot and cold flow is exchangeable; several foils made with different materials (copper, peek, stainless steel and aluminum) and with different thickness have been investigated in order to put in evidence the effect due to the axial wall-fluid conjugate heat transfer on the thermal efficiency of the micro heat exchanger. The results show that the conjugate heat transfer can be very strong in micro heat exchangers and it tends to reduce the effectiveness of counter-current micro heat exchangers and to increase the effectiveness of cross flow micro heat exchangers. In the case of a co-current arrangement with balanced flows the role of the wall axial conduction can be considered negligible.