Flow Micro Research Articles

Comparative analysis of biogas and yields from cattle, sheep, poultry wastes and their combinations

Comparative analysis of biogas yields from cattle, sheep and poultry wastes and blends were carried out at mesophilic temperature range (30oC–40oC) in a laboratory scaled conventional digestive system coupled with batch flow micro digesters. The system was made of air – impermeable plastic containers with effective volume of 4 l. Experiments were carried out in three replicates and at varying total solid concentrations (5%, 15% and 25%) and monitored for 8 days detention period (anaerobically digested); one day lag period observed for bacteria activation on the slurries. Biogas yields were compared as well as the variation of the total solid (TS) concentrations with together with their combinations. Seven batch type anaerobic laboratory-scale digesters were used. Biogas measurement was by water displacement method. Hydrogen ion concentration, ash content of the pulverised materials before and after digestion were determined. Results showed that the composite blends of the three livestock (cattle + sheep + poultry) wastes have the highest biogas potential at 15% total solids concentration which peaked during the fourth day. There was a significant difference at 5% confidence level (P > .05) between the digestion of carbon before and after digestion and hence increase in C:N ratio was observed which favoured complete digestion with positive correlation of all the proximate analysis parameters before and after digestion.

Amino-Modified Silica-Supported Copper-Palladium Alloy. Synthesis and Use in Selective Hydrogenation of Disubstituted Nitroarenes in a Flow Micro Reactor

A copper-palladium catalyst supported on amino-modified silica has been synthesized by chemical reduction. It has been found that submicron particles of a copper-palladium alloy are formed on the silica surface. Unlike commercially available palladium catalysts (Pd/Al2O3, Pd/C, Pd/BaSO4), the synthesized copper-palladium catalyst makes it possible to selectively reduce the nitro group in 3-nitrobenzaldehyde and 1-chloro-4-nitrobenzene.

Numerical Evaluation of Pollutants Emissions in a Homogeneous Methane/Air Micro Flame

Exhausting pollutant gas in a plug flow micro reactor are identified, described and predicted in this paper. For this, a premixed methane/air micro flame was simulated by a simplified chemical kinetics mechanism with four equations of Jones and Lindstedt. In addition to the Jones and Lindstedt model, one chemical kinetic mechanism with three equations describing the formation of thermal NO was integrated in Comsol 4.2a code, all that equations describing the production process and disappearance of the major chemical species. Simulations in stoichiometric and lean conditions with equivalent ratio ф equal to 0.9 and 0.7 show that the simulations with Jones and Lindstedt model provide a stable flame with the temperatures of the same order as that obtained with a detailed chemical kinetic mechanism as reported in the literature. Production of carbon dioxide (CO2) varies with the richness of the mixture. It is high with ф = 1 and in the order of 250 ppm, this value remains smaller than the required threshold for breathable air. Carbon monoxide (CO) is not found in the products of combustion due to the high temperatures at the outlet of the microreactor in the three cases

Induced mixing electrokinetics in a charged corrugated nano-channel: towards a controlled ionic transport

To perform a fluid analysis for electroosmotic flows in micro- and nano-channels, it is necessary to mix various fluid contents in micro- and nano-scales. It is observed that fluids in electroosmotic flow exhibits Reynolds number effect as the flow exerts very weak inertial force and it requires long channel for mixing of different layers and species through diffusion process. Hence, if the desired length scale of mixing is large, an enormous time is needed for the molecules to be thoroughly mixed by diffusion. The theory of dynamic equations on time scale is used to study the stability of these systems. It is found that such a system may exhibits an unstable nature for overlapping electric double layer field with fluctuating velocities and stability is preserved for zero linear growth coefficient. To obtain an improved understanding of mixing performance, a numerical study is performed with the variation of channel height when more than one ionic species with channels patterned with heterogeneity is considered. The wall heterogeneity may be created by placing some blocks of unequal size (with or without charged) close to the channel wall or some external potential patches. The analytical results for the transport characteristics of electroosmotic flow obtained are compared with the direct numerical simulation of the Navier–Stokes equation, Nernst–Plank equation, and Poisson equation, simultaneously. It is shown that heterogeneous potential could generate complex flow structures and the increment of species layers at different levels of the channel cross section from inlet to outlet significantly improve the mixing rate.

Simulation of the head-disk interface gap using a hybrid multi-scale method

We present a hybrid multi-scale method that provides a capability to capture the disparate scales associated with modelling flow in micro- and nano-devices. Our model extends the applicability of an internal-flow multi-scale method by providing a framework to couple the internal (small scale) flow regions to the external (large scale) flow regions. We demonstrate the application of both the original methodology and the new hybrid approach to model the flow field in the vicinity of the head-disk interface gap of a hard disk drive enclosure. The internal flow regions within the gap are modelled by an extended internal-flow multi-scale method that utilises a finite-difference scheme for non-uniform grids. Our proposed hybrid multi-scale method is then employed to couple the internal micro-flow region to the flow external to the gap, to capture entrance/exit effects. We also demonstrate the successful application of the method in capturing other localised phenomena (e.g. those due to localised wall heating).

A novel kinetic-based slip velocity boundary condition suitable for compressible gas flows in micro-/nanochannels

Micro-/nanoscale gaseous flow are widely used in various industrial applications such as micro-/nanosensors, hard disk drives, etc. The purpose of the current paper is to introduce a novel slip velocity boundary condition for any flat channels gas flow that are in slip flow regime or early transition flow regime. The new boundary condition is driven from the kinetic-based modification of Navier–Stokes equation. Stress tensor in the Navier–Stokes equation is modified by using the solution of the Boltzmann equation. The present slip model shows analytically how the slip velocity boundary condition is affected not only by the axial pressure gradient but also by the compressibility of gas. The new boundary condition is verified with the main reference experimental data and numerical results of Boltzmann equation in the isothermal gas flow between two long parallel plates. The results of mass flow rate and velocity show improvement due to considering compressibility of gas.

Numerical simulation of Al2O3 – water nanofluid effects on the performance of a cross flow micro heat exchanger

The numerical model investigated in this paper was implemented with Finite Element Method (FEM) based Comsol Multiphysics software, starting from a real cross-flow micro heat exchanger manufactured from 50 stainless steel plates for cold and hot fluid transfer. Each plate (foil) had 34 microchannels with rectangular cross-section, at a depth of 100 μm and a width of 200 μm. The working fluids were water and Al2O3-water nanofluids with volumetric concentrations of 0.5%, 1% and 1.5% in the temperature domain of 293 – 333 K. The oxide-based nanofluids are widely investigated in thermal energy transfer applications due to an increased heat transfer performance by comparing with pure water as a cooling fluid. Analytical models for the physical properties of water and nanofluid, referring to density, viscosity, thermal conductivity and specific heat capacity were used here. Microchannel bulk temperature profiles for cold and hot plates of the model with 1% Al2O3-water nanofluid were presented here in order to examine the uniformity of temperature distribution in the channel flow field area. Simulation results indicated that the total heat flow rate in the heat exchanger models increased with the increase in volume concentration of the nanoparticles at mass flow rates of 41, 61, 81, 101 and 150 Kg/h, but with the expense of a bigger pressure drop (or Fanning friction factor) at an increased pumping power required to drive flow through the channels.

Solvent‐Free Synthesis of Bismuth Oxychloride Microflower/Nanosheet Homojunctions for Photoactivity Enhancement

AbstractSolvent‐free synthesis of bismuth‐based photocatalysts with hierarchical architectures has been rarely reported yet. Herein, BiOCl hierarchical microflowers (MFs) were prepared via a solvent‐free route for the first time, using chlorobutanol as the chlorine source. The reaction temperature (T) plays a key role for formation of MFs. The MFs were formed at T >120 °C and some MFs merged into large nanosheets (LNs). MF/LN homojunctions were constructed because considerable differences in sizes and exposed facets between the MFs and the LNs cause differences in their energy band levels. The sample prepared at 120 °C possesses the highest contents of MFs and homojunctions, specific surface area (SBET, 13 m2 g−1), and photoactivity, indicating the high photoactivity of the sample arises from fabrication of homojunctions as well as the high SBET. This work provides a solvent‐free way to simultaneously synthesize BiOCl MFs and homojunctions, which paves an avenue for solvent‐free synthesis of other photocatalysts.

ESTIMATION OF THE SLIP LENGTH IN THE FLOW OF LIQUID IN MICRO-CHANNELS

Research review of phenomenon for slip flow in micro and nanocannels is presented in the paper. The analysis of theoretical and experimental data characterizing the slip length is carried out. In slip flow in microchannels the slip length is affected by the contact angle of the liquid with the surface, shear stress, pressure, dissipative heating, the amount and nature of the dissolved gas in the liquid, electrical characteristics, surface roughness. Studies of flow in microchannels with hydrophobic walls, which are based on molecular dynamics, showed that the slip length has order of 20 nm. This is much less than the values observed in the experiment. The introduction of an effective (apparent) slip length suggests the existence of a thin layer of gas bubbles near the hydrophobic surface or liquid layer with low value of viscosity and density. Since the idealized model for the total coverage of a hydrophobic surface by gas bubbles gives, as a rule, overestimated values of the slip length in comparison with experimental ones, some researchers consider the inhomogeneous coating of the wall by gas bubbles. In this case, the effect of a layer with a lower viscosity on the slip length turns out to be weaker.

Excess molar enthalpies of n-alkanol (C2-C10) with n-decane at 298.15 K: Flory–Treszczanowicz–Benson model

Excess enthalpies and excess volume for n-alkanol (C2-C10) (1) + n-decane (2) mixtures were measured at 298.15 K using flow micro calorimeter. The excess enthalpy for equimolar binary mixtures varies as: propanol ≈ butanol > pentanol > ethanol > hexanol > heptanol > octanol > nonanol > decanol. The Redlich-Kister polynomial was used to correlate the experimental data. The Mecke-Kempter type of association model for alkanol proposed by Treszczanowicz and Benson was applied to predict excess enthalpy and excess volume data of the present systems. The predicted data compared well with the measured excess enthalpy and previously reported excess volume data.

Fractal analysis of the effect of rough surface morphology on gas slip flow in micro- and nano- porous media

Gas slip flow in micro- and nano- porous media with rough surfaces is investigated by the fractal geometry theory with a focus on the effect of surface roughness of capillaries. Based on the assumption that the pore size distribution of the porous media and rough elements of the wall surfaces of capillaries follow the fractal scaling law, apparent gas permeability and gas slippage factor are derived. According to the Klinkenberg equation, the key to the calculation of apparent gas permeability is the determination of gas slippage factor. In this paper, we established an analytical relationship between the gas slippage factor and the structural parameters of porous media. We first validated the model with available experimental data, then analyzed the effect of the relative roughness, porosity, the tortuosity fractal dimension and the pore fractal dimension on the gas slippage factor. With our fractal model, the physical mechanisms of gas slip flow are better elucidated.

Numerical analysis of solid liquid two phase abrasive flow polishing process for three stage variable diameter pipe

With the rapid development of technology and economy, rough machining has not been able to keep pace with the times. Heavy industry is more and more inclined to the field of precision and ultra-precision machining. During that time, abrasive flow machining technology emerged as the times require. The process of micro cutting is achieved through the contact between abrasive particles and workpiece, so that the accuracy of workpiece's inner surface can be polished, and the accuracy of workpiece improved, which is a representative polishing method. Taking the three-order variable diameter tube as the research object, this paper discusses the polishing characteristics of three level variable diameter pipe with solid liquid two phase abrasive flow. The removal pattern of abrasive flow micro cutting is analyzed, with the collision effect between abrasive particles and wall considered and ignored, which provides technical support for abrasive flow polishing variable diameter pipe parts.

Morphology-controlled synthesis of 3D flower-like NiWO4 microstructure via surfactant-free wet chemical method

Three-dimensional (3D) flower-like controllable microstructures of nickel tungsten oxide (NiWO4) were synthesized by using a surfactant free wet chemical method at low temperature (60 °C). The uniform morphologies of NiWO4 were molded by adjusting the temperature, stirring rate, and dosage of hydrazine in aqueous solution. We reported immediate precipitation of the 3D NiWO4 microflowers (MFs) by introducing hydrazine monohydrate (N2H4·H2O). This approach resulted in a better yield and shortened the reaction time. In this work, we investigated the probable mechanism behind the formation of flower-like microstructures. Furthermore, the flower-like microstructure was assessed for its electrochemical properties towards non-enzymatic glucose sensing by addition of 50 μL of a glucose solution (50 μM) in an electrolyte (0.1 M NaOH) using glassy carbon electrode.

Modelling the synthesis of nanoparticles in continuous microreactors: The role of diffusion and residence time distribution on nanoparticle characteristics

A mathematical model for the liquid-phase synthesis of spherical nanoparticles in continuous flow micro- and milli-reactors was developed, accounting for residence time distributions (RTD). These distributions were derived for the reactants and the particles involved in the synthesis. The kinetic parameters needed to describe the reactions were calculated from experimental data available in the literature from batch reactors, with the aid of population balance modelling. They were subsequently used, without further modification, to simulate the synthesis in flow reactors via population balance modelling, averaging the nanoparticle properties at the reactor outlet using the reactor RTDs. The model was employed to describe the synthesis of silica nanoparticles as a case study, and validated against flow reactor results from the literature. The results demonstrate direct RTD effects and indirect diffusion-induced effects on the evolution of the particle size distribution during the flow synthesis. The former are created by the inherent widening of the RTDs, due to the different residence time experienced by each fluid element, leading to a broadening of the particle size distribution. The latter are induced by the difference in diffusivity between nanoparticles and liquid reactants, which leads to different dispersion processes in the reactor for the different components of the reaction mixture. These effects appear as the major cause of particle size distribution difference between (single phase) flow and batch syntheses.

Analysis of the dynamic characteristics of air-water two-phase flow in small channel based on multi-scale normalized Benford probability distribution

In gas and liquid two-phase flow, different flow patterns show their unique nonlinear dynamic characteristics due to the complex interaction between them. To further reveal the underlying dynamic characteristics of this physical phenomenon, this paper presents a new model for the analysis of small channel gas-liquid two-phase flow pattern signals based on the multi-scale normalized Benford probability distribution (MSNBPD) analysis. The first focus area is the difference between the characteristics of a multi-scale approach to Benford’s probability distribution and Benford’s Law (BL) distribution in a typical nonlinear system. Once the terms are defined, the authors show how BL could be applied in a multi-scale based flow-pattern based method to analyze differential pressure signals of gas-liquid two-phase flow in small channels to reveal the underlying dynamic characteristics of different gas-liquid two-phase flow patterns, and their sensitivity to scale changes. In addition, the stability of different flow patterns was revealed by the variable scale range calculation. Flow patterns could then be distinguished based on Euclidean distance and the variable scale range difference of differential pressure signals. This paper also compares the present method with other methods that have been used in flow identification. The results show that this new method can well distinguish nonlinear systems with different dynamic mechanisms. This method can also reveal the underlying dynamic characteristics of a gas-liquid two-phase flow of micro and small channels. The two characteristic values (Euclidean distance and variable scale range difference) proved to be a good distinction for two-phase flow patterns than other time and frequency methods, with several possible universal applications. However, the identification results of micro and small channels were better than that of regular pipe, which shows that this method is more suitable for the identification of micro and small channel flow.

Особливості тепломасообміну в ламінарних течіях мікро і нанорідин по трубках і каналах

In recent years, high efficiency of using suspensions of nanoparticles for cooling of the operating systems compared to a homogeneous liquid has been shown, and the parameters of suspensions effective for various specific devices have been selected in experiments. A brief review of the relevant experimental data, as well as mathematical models of the flow of micro- and nanofluids, based on the incompressible Navier-Stokes equations with boundary conditions accounting for tangential momentum transfer of the particles and temperature jump due to diffuse reflection at rough walls, are presented. For the case of a laminar flow between infinite parallel plates with constant heat fluxes through the plates, an analytical solution is obtained for the velocity and temperature fields. Numerical calculations showed that with an increase in the momentum transfer coefficients at the plates, the flow accelerates significantly, which contributes to an increase in volumetric flow with the same pressure drop across the channel due to a decrease in the shear stress at the wall. Correspondingly, the heat transfer through the plates and the heat removal with the fluid flow increase. Based on the obtained analytical relationships, it is possible to select the parameters of the plate surfaces in such a way as to optimize the system, for example, to reduce the energy loss due to viscous and thermal dissipation or to obtain uniform temperature distributions in the liquid with asymmetric heat flows through the plates.

Dimensional tailoring of hydrothermally grown zinc oxide nanostructures in a continuous flow micro reactor.

Dynamic deposition of ZnO nanostructures with varying morphologies (nanorods, nanocones, nanopencils, nanosheets, etc.), diameters, lengths and aerial densities on ITO-PET substrates has been achieved using a continuous flow microreactor in which we maintained a homeostatic zinc concentration and varied the other reactants' concentrations.

Heat Transfer Enhancement in Ferrofluids Flow in Micro and Macro Parallel Plate Channels: A Comparative Numerical Study

This paper presents a comparative numerical study of heat transfer enhancement in steady, laminar, hydrodynamically fully developed flow of water-based ferrofluids under no magnetic field in micro and macro parallel plate channels subjected to constant equal heat fluxes on its top and bottom, considering Brownian diffusion and thermophoresis of ferroparticles in the base fluid. While the microchannel results match very well with the experimental data for water in an equivalent microtube (Kurtoglu et al., 2014, “Experimental Study on Convective Heat Transfer Performance of Iron Oxide Based Ferrofluids in Microtubes,” ASME J. Therm. Sci. Eng. Appl., 6(3), p. 034501.), the numerically predicted enhancement factor in ferrofluids is much below that for the same microtube. A detailed parametric study points to possible inaccuracies in the experimental results of Kurtoglu et al. (2014, “Experimental Study on Convective Heat Transfer Performance of Iron Oxide Based Ferrofluids in Microtubes,” ASME J. Therm. Sci. Eng. Appl., 6(3), p. 034501.) for ferrofluids. The nanoparticle concentration profiles in the microchannel flow reveal that (a) the nanoparticle concentration at the wall increases with axial distance, (b) the wall nanoparticle concentration decreases with increasing heat flux, and (c) the concentration profile of nanoparticles is parabolic at the exit. A comparison of thermally developing flow in microchannel and macrochannel of the same length (0.025 m) indicates that the enhancement factor at the microchannel exit is 1.089 which is only marginally higher than that at the macrochannel exit in the heat flux range of 20–80 kW/m2. On the other hand, for the thermally fully developed flow in both microchannel and macrochannel of the same length (0.54 m) the maximum enhancement factor for the macrochannel is 1.7, as compared to 1.1 for the microchannel, in the heat flux range of 1–4 kW/m2.

Flow control in Banki turbines

Cross flow micro turbines are environmentally friendly equipment. A low head Banki turbine is studied in this paper numerically and experimentally in order to identify the reasons why the turbine efficiency is poor at low rotational speeds. A procedure that consists in dividing the flow domain into different zones is proposed for clarifying the main issues. The turbine efficiency obtained experimentally is explained based on a CFD analysis that highlights the influence of recirculation phenomena and shock losses produced when the water jet impinges on the shaft. This analysis is also used to propose a device for internal flow control.

Wear and Tear of Tyres: A Stealthy Source of Microplastics in the Environment.

Wear and tear from tyres significantly contributes to the flow of (micro-)plastics into the environment. This paper compiles the fragmented knowledge on tyre wear and tear characteristics, amounts of particles emitted, pathways in the environment, and the possible effects on humans. The estimated per capita emission ranges from 0.23 to 4.7 kg/year, with a global average of 0.81 kg/year. The emissions from car tyres (100%) are substantially higher than those of other sources of microplastics, e.g., airplane tyres (2%), artificial turf (12–50%), brake wear (8%) and road markings (5%). Emissions and pathways depend on local factors like road type or sewage systems. The relative contribution of tyre wear and tear to the total global amount of plastics ending up in our oceans is estimated to be 5–10%. In air, 3–7% of the particulate matter (PM2.5) is estimated to consist of tyre wear and tear, indicating that it may contribute to the global health burden of air pollution which has been projected by the World Health Organization (WHO) at 3 million deaths in 2012. The wear and tear also enters our food chain, but further research is needed to assess human health risks. It is concluded here that tyre wear and tear is a stealthy source of microplastics in our environment, which can only be addressed effectively if awareness increases, knowledge gaps on quantities and effects are being closed, and creative technical solutions are being sought. This requires a global effort from all stakeholders; consumers, regulators, industry and researchers alike.