Laboratory model studies of flushing of trapped salt water from a blocked tidal estuary

Results are presented from a series of laboratory model studies of the flushing of saline water from a partially- or fully-closed estuary. Experiments have been carried out to determine quantitatively the response of the trapped saline volume to fresh water flushing discharges Q for different values of the estuary bed slope α and the density difference (∆ρ)_o between the saline and fresh water. The trapped saline water forms a wedge within the estuary and for maintained steady discharges, flow visualisation and density profile data confirm that its response to the imposition of the freshwater purging flow occurs in two stages, namely (i) an initial phase characterised by intense shear-induced mixing at the nose of the wedge and (ii) a relatively quiescent second phase where the mixing is significantly reduced and the wedge is forced relatively slowly down and along the bed slope. Scalings based upon simple energy balance considerations are shown to be successful in (i) describing the time-dependent wedge behaviour and (ii) quantifying the proportion of input kinetic energy converted into increasing the potential energy of the wedge/river system. Measurements show that the asymptotic value of the energy conversion factor increases with increasing value of the river Froude number Fr_o at small values of Fr_o, thereafter reaching a maximum value and a gradual decrease at the highest values of Fr_o. Dimensional analysis considerations indicate that the normalised, time-dependent wedge position (x_w)³(g')o/q² can be represented empirically by a power-law relationship of the form (x_w)[(g')_o/q²]^1/3 =C [(t)[(g')_o²/q]^1/3]"where the proportionality coefficient C is a function of both Fr_o and the slope angle α and the exponent n has a value of 0.24. Successful attempts are made to relate the model data to existing field observations from a microtidal estuary.

Experiments with multiple, intermittent periodic flushing flows confirm the importance of the starting phase of each flushing event for the time dependent behaviour of the saline wedge after reaching equilibrium in the intervals between such events. For the parameter ranges investigated and for otherwise-identical external conditions, no significant differences are found in the position of the wedge between cases of sequential multiple flushing flows and steady single discharges of the same total duration.

Characterization on ferrite microstructure evolution during large strain warm torsion testing of plain low carbon steel

Ferrite grain/subgrain structures evolution during the extended dynamic softening of a plain low carbon steel was investigated throughout the large strain warm deformation by hot torsion. Microstructural analysis with electron back-scattering diffraction (EBSD) scanning electron microscope (FEG/SEM) was carried out on the ferrite microstructural parameters. The results showed that the warm flow stress–strain curves are similar to those affected only by dynamic softening and an extended warm flow softening is seen during large strain deformation up to 30. Furthermore, with an increase in strain up to ~ vert, similar1 the grain size of ferrite, misorientation angle and fraction of high-angle boundaries gradually decrease and fraction of low-angle boundaries increases. With a further increase in the strain beyond ~, vert, similar2, these parameters remain approximately unchanged. No evidence of discontinuous dynamic recrystallisation involving nucleation and growth of new grains was found within ferrite. Therefore, the dynamic softening mechanism observed during large strain ferritic deformation is explained by continuous dynamic recrystallization (CDRX).

Micro- and nano-characterization of membrane materials

The global warming has led to enormous challenges worldwide for a large variety of communities, particularly these associated to water and water treatment industry. Due to increasing scarcity of water resources, the development of new membrane materials and water treatment processes will play an important role in tackling this emerging problem. In this paper, the recent development in characterization of in particular, geometrical parameters of micro- and nano-membrane materials will be reviewed. Membranes with micro- and nano-pores have widely been used for ultrafiltration and nanofiltration. The structure of the pores and the surface of the pores/membranes may be optimized to achieve much improved flow rate in these micro-/nano-channels. Therefore, accurate characterization of porous structures will contribute significantly to the prediction of membrane performance. It will not only provide an insight into the new characterization methods but also the development of novel materials.

Characterization of high fluid strain micro contractions to study the stress on biological fluids

Microfluidics has the potential to enhance the understanding of the biological fluids under strain, due to the laminar nature of the fluid and the possibility to mimic the real conditions. We present advances on charaterization of a microfluidic platform to study high strain rate flows in the transport of biological fluids. These advances are improvements on the reproduction of a  constant extensional strain rate using micro contractions and development of 3D numerical models. The micro geometries have been fabricated in polydimethyl siloxame (PDMS) using standard soft-lithography techniques with a photolithographically patterned mold. A comparison of some microcontractions with different funnel characteristics is presented. The Micro Particle Image Velocimetry technique has been applied to validate the numerical simulations. We demonstrate the use of microfluidics in the reproduction of a large range of controllable extensional strains that can be used in the study of the effect of flow on biological fluids.

Hydrodynamic flow focusing to study the isolated effects of the flow components

Biological fluids such as blood, proteins and DNA solutiosn moving within fluidic channels can potentially be exposed to high level of shear, extension or mixed stress, either in vitro such as industrial processing of blood products or in vivo such as ocurrs in some pathological conditions. This exposure to a high level of strain can trigger some reactions. In most of the cases the nature of the flow is mixed with shear and extensional components. The ability ot isolate the effects of each component is critical in order to understand the mechanisms behind the reactions and potentially prevent them. Applying hydrodynamic flow focusing, we present in this investigation the characterization of microchannels that allow study of the regions of high shear or high extension strain rate. Micro channels were fabricated in polydimethyl siloxane (PDMS)  using standard soft-lithography techniques with a photolithographically patterned mold. Characterization of the regions with high shear and high extension strain rate is presented. Computational Fluid Dynamics (CFD) simulations in three dimensions have been carried out to gain more detailed local flow information, and the results have been validated experimentally. A comparison between the numerical models and experiment and is presented. The advantages of microfluidic flow focusing in the study  of the effects of shear and extension strain rates for biological fluids are outlined.

Design, characterization and application of a novel mono-layer pin-microvalve for microfluidic devices

Valves are one of the key components in microfluidic devices to control the fluid flow. In this paper we introduce a novel manual pin-valve which can operate in both analogue (partially close) and digital (on/off) states. We also demonstrate implementation of this pin-valve in a hydrodynamic flow focusing (HFF) device. © The Royal Society of Chemistry 2014.

Non-contact measurement of respiratory function and deduction of tidal volume

 This paper further the investigation of Doppler radar feasibility in measuring the flow in and out due to inhalation and exhalation under different conditions of breathing activities. Three different experiment conditions were designed to investigate the feasibility and consistency of Doppler radar which includes the combination of the states of normal breathing, deep breathing and apnoea state were demonstrated. The obtained Doppler radar signals were correlated and compared with the gold standard medical device, spirometer, yielding a good correlations between both devices. We also demonstrated the calibration of the Doppler radar signal can be performed in a simple manner in order to have a good agreements with the spirometer readings. The measurement of the flow in and out during the breathing activities can be measured accurately under different dynamics of breathing as long as the calibration is performed correctly.

Inquisition of Microcystis aeruginosa and Synechocystis nanowires: characterization and modelling

Identification of extracellular conductive pilus-like structures (PLS) i.e. microbial nanowires has spurred great interest among scientists due to their potential applications in the fields of biogeochemistry, bioelectronics, bioremediation etc. Using conductive atomic force microscopy, we identified microbial nanowires in Microcystis aeruginosa PCC 7806 which is an aerobic, photosynthetic microorganism. We also confirmed the earlier finding that Synechocystis sp. PCC 6803 produces microbial nanowires. In contrast to the use of highly instrumented continuous flow reactors for Synechocystis reported earlier, we identified simple and optimum culture conditions which allow increased production of nanowires in both test cyanobacteria. Production of these nanowires in Synechocystis and Microcystis were found to be sensitive to the availability of carbon source and light intensity. These structures seem to be proteinaceous in nature and their diameter was found to be 4.5-7 and 8.5-11 nm in Synechocystis and M. aeruginosa, respectively. Characterization of Synechocystis nanowires by transmission electron microscopy and biochemical techniques confirmed that they are type IV pili (TFP) while nanowires in M. aeruginosa were found to be similar to an unnamed protein (GenBank : CAO90693.1). Modelling studies of the Synechocystis TFP subunit i.e. PilA1 indicated that strategically placed aromatic amino acids may be involved in electron transfer through these nanowires. This study identifies PLS from Microcystis which can act as nanowires and supports the earlier hypothesis that microbial nanowires are widespread in nature and play diverse roles.

Tow testing of Savonius wind turbine above a bluff body complemented by CFD simulation

A simple way to improve its power coefficient (cp) of a Savonius turbine is by its installation above a cuboidal building as the building will redirect the wind and increase its speed significantly. To determinethe gain, a turbine was constructed and installed above a bluff body and tow tested. Detailed measurements of vehicle speed and turbine power were made. Tow test speeds were 8, 10 and 12 m/s, while TSR range was 0.6-1.1. Most importantly, wind speed at the position beside and slightly above the turbine was measured during test runs. The cp calculated using this measured wind speed was used to validate CFD simulation results. Simulation results were also used to obtain the relationships between the wind speed of the free stream and at the anemometer position. Typically, wind speed at the anemometer position is about 9% higher than those of the free stream. These relationships were used to derive the free stream wind speed of each experimental run. The cp calculated using these derived free stream wind speeds showed an increase of 25% at 12 m/s wind speed, compared to the cp reported by previous researchers for a similar turbine operating in unmodified air flow.

Numerical simulation of a Savonius turbine above an infinite-width forward facing step

The Savonius turbine, although simple in construction, typically has a maximum power coefficient (cP) of about 0.2. This is significantly lower than the cP of the axial flow propeller-type turbine which typically can be as high as 0.5. However, a simple means to improve the cP of a Savonius turbine is to install it above a forward facing step, for example, a cliff or a building. In this work, prior experimental results of the tow testing of a Savonius turbine installed above a finite-width bluff body were used to validate computational fluid dynamics simulation of the same experimental conditions. The validated simulation settings were then used to obtain the maximum cP of a similar turbine of finite width but installed above an infinite-width forward facing step over a range of installation positions above and behind the step.

Study of KJ-66 micro gas turbine compressor: steady and unsteady Reynolds-averaged Navier-Stokes approach

Numerical study on the compressor stage of a KJ-66 micro gas turbine was conducted in this paper through both steady and unsteady Reynolds-averaged Navier–Stokes. The study was conducted for the numerical prediction of micro gas turbine compressor performance at various operation conditions, with special attention given to the transient flow behaviors during compressor operation. The numerical results showed reasonable agreements with experimental data while providing predictions for the charting of compressor performance map at various operation speeds. The simulation results indicated that the increase of operation speed from 80 k r/min to 117 k r/min would leads to an increased peak total pressure ratio from 1.54 to 1.96, while decreasing the peak adiabatic efficiency from 0.73 to 0.55. This paper also provided discussion on details of transient flow field within the compressor stage as well as demonstrated the smooth flow transition through rotor–stator interactions.

Numerical investigation of the turbulent energy budget in the wake of freely oscillating elastically mounted cylinder at low reduced velocities

We present a numerical study of the turbulent kinetic energy budget in the wake of cylinders undergoing Vortex-Induced Vibration (VIV). We show three-dimensional Large Eddy Simulations (LES) of an elastically mounted circular cylinder in the synchronization regime at Reynolds number of Re=8000. The Immersed Boundary Method (IBM) is used to account for the presence of the cylinder. The flow field in the wake is decomposed using the triple decomposition splitting the flow variables in mean, coherent and stochastic components. The energy transfer between these scales of motions are then studied and the results of the free oscillation are compared to those of a forced oscillation. The turbulent kinetic energy budget shows that the maximum amplitude of VIV is defined by the ability of the mean flow to feed energy to the coherent structures in the wake. At amplitudes above this maximum amplitude, the energy of the coherent structures needs to be fed additionally by small scale, stochastic energy in form of backscatter to sustain its motion. Furthermore, we demonstrate that the maximum amplitude of the VIV is defined by the integral length scale of the turbulence in the wake