Switching Of Flow Direction Research Articles

Electrical properties determine the liquid flow direction in plasma–liquid interactions

During atmospheric pressure plasma impingement, plasma induced liquid flow will influence the transport and distribution of plasma generated charged and reactive species in liquids. We use particle image velocimetry and supplementary pH, conductivity and temperature measurements to investigate electrical properties of an AC kHz plasma jet interacting with water and electrolytes. We observe that the dominant driving mechanism in low conductive solutions are surface forces such as shear stresses and stagnation-pressure induced dimpling. These give upwards flows beneath the plasma–liquid interaction point. In highly conductive solutions, such as water with dissolved salts, the dominant driving mechanism is electro-hydrodynamic forces, with flows directed downwards underneath the plasma jet in our system. We therefore demonstrate that the direction of initial plasma induced liquid flows can be controlled through the addition of salt ions. In electrically grounded salt solutions, we also observe time resolved flow direction switching, possibly due to modification of salt solutions via electrolytic and plasma induced reactions changing the dominant flow mechanism over time.

Selective directional liquid transport on shoot surfaces of Crassula muscosa.

Directional liquid transport has been widely observed in various species including cacti, spiders, lizards, the pitcher plant Nepenthes alata, and Araucaria leaves. However, in all these examples the liquid transport for a specific liquid is completely restricted in a fixed direction. We demonstrate that Crassula muscosa shoot surfaces have the ability to transport a specific liquid unidirectionally in either direction. This is accomplished through the presence of asymmetric reentrant leaves with varying reentrant angles, which yields the variation in liquid meniscus heterogeneity. These findings enable engineered biomimetic structures capable of selective directional liquid transport, with functions such as intelligent flow direction switching, liquid distribution, and mixing.

Inactivation of helminth eggs in an electro-Fenton reactor: Towards full electrochemical disinfection of human waste using activated carbon

The disinfection of helminth eggs and Escherichia coli contaminated aqueous solutions, was studied using an electro-Fenton reactor equipped with a polarized activated carbon (AC) packed bed and two chambers loaded with cation exchange resins. Experiments using different arrangements and operation conditions, revealed that effective elimination of Escherichia coli takes place in all electrochemical disinfection tests. For the more resistant helminth eggs however, adsorption, electro-oxidation and electro-Fenton experiments showed retention within the reactor and pathogen inactivation values of 0, 16, and 25%, respectively. Using helminth eggs concentration data in different sections of the reactor, optical microscopy analysis and an exploratory computer simulation, differences in the disinfection performance were explained and new recirculation and flow direction and polarization switching operation schemes were defined. The corresponding experiments revealed that the effective coupling between adsorption and electro-Fenton phenomena, all along the AC packed bed compartment, results in 100% inactivation of helminth eggs.

Switchable Direction of Liquid Transport via an Anisotropic Microarray Surface and Thermal Stimuli.

Design and construction of special surface microstructures has made many amazing breakthroughs in directional liquid transport. Despite much progress in this field, challenges still remain in on-demand switchable direction transport of liquid in situ and real-time via transforming the arrangement of the surface microstructure and external stimuli. Herein, we demonstrate a strategy to achieve switchable direction transport of liquid via a tunable anisotropic microarray surface, that is, assembling a V-shaped prism microarray (VPM) surface, which can also be intelligently manipulated by thermal stimuli. By transforming the parallel and staggered prism microstructure arrangement of the VPM, switchable direction transport of a liquid can be successfully achieved on the VPM surface. Flow direction switching among unidirectional transport, bidirectional transport, and reverse unidirectional transport is also achieved on the temperature-adaptive VPM surface by thermal stimuli, which can be used for on-demand liquid transport according to the paths of the microfluidic channels. The work provides a way for precise liquid manipulation in desired liquid transport, which may be utilized in nonpower conveying systems, autolubrication, life fluid medical instruments, and other microfluidic devices.

De-icing of fuel/oil heat exchange systems via fuel flow direction switching device

Fuel icing of fuel/oil heat exchange systems has been a troublesome issue. In this study, a de-icing method is proposed to manage the fuel icing problem by switching the fuel flow direction of the systems. This method uses the fuel/oil heat exchanger as a passive heat source, heat and momentum of the fuel are delivered to the ice. A device named FFDSD (Fuel flow direction switching device) has been developed for this method. This device consists of two normally open and two closed type solenoid valves, and the proposed configuration consumes electrical power only when switching fuel flow directions (36 W to 0 W). A control algorithm has been developed as a countermeasure against a large amount of ice inflow that conventional methods cannot cope with. FFDSD was designed and fabricated, and the experimental test was conducted. The experimental results show that the proposed method can successfully achieve the de-icing of the fuel system within 1 s. A numerical de-icing process was attempted. Ice in fuel was numerically modeled as a fluidized quasi-solid material based on descriptions in previous studies. Numerical analysis results show a similar tendency to experimental results. The results of this study would be useful to manage fuel icing problem of heat exchange systems.

Smart Liquid Transport on Dual Biomimetic Surface via Temperature Fluctuation Control

AbstractMicrodevices that manipulate fluids to transport in a predefined direction and to switch flow directions under temperature stimuli are fundamental to the intelligent control of biomedical devices, thermal managements, lab‐on‐a‐chip, etc. Despite current advances in controlling drop transport, the amplitude of liquid motion is still limited with a low speed, and the flow direction is not well controlled because of the pinning of contact lines on surface defects. Learning from nature, here, two bioinspired principles derived from the peristome surface of the pitcher plant and the beak of the shorebird are fused into a composite, and a peristome–beak mimetic surface is fabricated with flow direction switching between uni‐ and bidirections under temperature fluctuations. Significantly, deposited water can intelligently find the transport path by itself on temperature‐patterned surface. This smart peristome–beak mimetic surface would extend the bioinspired design with multi‐integrations and find use in medical, microfluidic, and heat‐transfer systems.

Geomorphology and till architecture of terrestrial palaeo-ice streams of the southwest Laurentide Ice Sheet: A borehole stratigraphic approach

A multidimensional study, utilising geomorphological mapping and the analysis of regional borehole stratigraphy, is employed to elucidate the regional till architecture of terrestrial palaeo-ice streams relating to the Late Wisconsinan southwest Laurentide Ice Sheet. Detailed mapping over a 57,400 km2 area of southwestern Saskatchewan confirms previous reconstructions of a former southerly flowing ice stream, demarcated by a 800 km long corridor of megaflutes and mega-scale glacial lineations (Ice Stream 1) and cross cut by three, formerly southeast flowing ice streams (Ice Streams 2A, B and C). Analysis of the lithologic and geophysical characteristics of 197 borehole samples within these corridors reveals 17 stratigraphic units comprising multiple tills and associated stratified sediments overlying preglacial deposits, the till thicknesses varying with both topography and distance down corridor. Reconciling this regional till architecture with the surficial geomorphology reveals that surficial units are spatially consistent with a dynamic switch in flow direction, recorded by the cross cutting corridors of Ice Streams 1, 2A, B and C. The general thickening of tills towards lobate ice stream margins is consistent with subglacial deformation theory and variations in this pattern on a more localised scale are attributed to influences of subglacial topography including thickening at buried valley margins, thinning over uplands and thickening in overridden ice-marginal landforms.

Modeling the effect of coke deposition in a heat integrated ethanol reformer

The dynamic performance of a reformer as a incorporating the catalyst deactivation at the reactor level is modelled by accounting a theoretical coking model. This model incorporates the effect of coke deposition on catalyst activity, diffusion resistance of reactants, and subsequently catalyst pore blockage. The influence of catalyst fouling on the conversion of the product of interest has been illustrated by coupling a rate equation for the formation of coke to the continuity equation for the main products. The transient coke uptake curves are shown to have two regions of kinetics controlled and diffusion controlled through internal effectiveness factor. The implications of varying pore size on the reactor performance through such curves are discussed. It is shown that small pore size (high surface to volume ratio) is not always efficient owing to rapid plugging. The energy intensive endothermic reaction system is coupled with an exothermic reaction to improve the thermal efficiency. The effect of this coupling on the coke formation and its implications on reactor performance is discussed incorporating the switching of species flow direction (co-flow and counter-flow) in combustion section.This modelling effort is unique is elucidating the spatial distribution of catalytic activity in a reformer, evolving owing to varying rates of local catalyst deactivation. Moreover, the simultaneous variation of catalyst activity and effective diffusivity have been modelled, which has never been investigated in the past. Conclusions from this work counter the often-maintained belief that enhanced heat transfer always enhance the reformer performance. We expect the broad conclusions of the modelling effort to direct future catalyst development.

Improved anammox performance with a flow switched anaerobic baffled reactor (FSABR) modified from a common anaerobic baffled reactor (CABR)

An anaerobic ammonium oxidation (anammox) reactor was operated with two feeding regimes. In stage 1, the reactor was operated as a common anaerobic baffled reactor (CABR) (constant flow direction), whereas in stage 2, the reactor was modified as a flow switched anaerobic baffled reactor (FSABR) with the flow direction switching every 10 days. Adjusting the feeding regime resulted in an increase in the average nitrogen loading rate (from 1.62 to 1.80kgNm−3d−1) and nitrogen removal efficiency (from 75.4 to 83.1%). In addition, a maximum nitrogen removal rate of 3.49kgNm−3d−1 was obtained in stage 2, compared with 3.00kgNm−3d−1 in stage 1. The sludge properties were also enhanced; from stage 1 to stage 2, the specific anammox activity increased by more than 5-fold, the settling velocity increased from 64.1 to 71.9mh−1, and the average particle diameter increased from 0.8 to 2.3mm. However, there was minimal variation in the heme c content. The maximum substrate removal rates in stages 1 and 2 were 4.28 and 46.38kgNm−3d−1 when fitted by the Stover-Kincannon model, respectively. The results indicate that the FSABR performance was significantly enhanced compared with the CABR.

Microfluidic control on nanoplasmonic thin films using Marangoni effect

The rapid switching of flow direction in a thin microfluidic chamber filled with water is demonstrated using the thermoplasmonic Marangoni effect. A gold island film is used as a thermoplasmonic heater on which a continuous-wave laser is focused to generate a microbubble and develop Marangoni flows around it. The direction of the observed flow significantly changes depending on the laser power. When the laser power is square-wave modulated, the flow direction instantaneously switches in response to the power, creating a discrete pattern of polystyrene microspheres. Flow direction-switching is observed for laser power modulation frequencies of up to 40 Hz, which indicates that the time constant of the flow direction switching is on the order of at least several milliseconds. This rapid flow direction switching is attributed to the fast response of both the thermoplasmonic effect of the gold nanoparticles and the Marangoni effect on the bubble surface.

Thermoresponsive switching of liquid flow direction on a two-face prism array

We present a simple approach to reversibly switch the direction of liquid flow on physically symmetric and chemically asymmetric prism structures by exploiting the reversibility of surface wetting properties of a thermo-responsive polymer, poly(N-isopropyl-acrylamide). Such an asymmetric prism array creates a flow path in the direction of the lower critical contact angle. This allows a unidirectional “step flow” across the ridges of prism channels, which can be made reversible with a suitable temperature change.

Methane autothermal reforming in a reverse flow reactor on Rh/Al2O3 catalyst

Autothermal reforming of methane was investigated in a Reverse Flow Reactor with commercial Rh/Al2O3 catalyst in pellets. The process was carried out in a catalytic fixed bed reactor and switching of feed flow direction was obtained through four electrovalves synchronized in pair. Temperature profile of the catalyst bed was measured by fast IR thermography and product composition was measured with a continuous gas analyzer.Reactor performance and catalyst temperature profile are presented as a function of feed direction switching period, water to methane inlet ratio and total inlet flow rate. Results are compared to steady state operation.

Switching of a paleo-ice stream in northwest Svalbard

Ice streams are the fast-flowing zones of ice sheets that can discharge a large flux of ice. The glaciated western Svalbard margin consists of several cross-shelf troughs which are the former ice stream drainage pathways during the Pliocene–Pleistocene glaciations. From an integrated analysis of high-resolution multibeam swath-bathymetric data and several high-resolution two-dimensional reflection seismic profiles across the western and northwestern Svalbard margin we infer the ice stream flow directions and the deposition centres of glacial debris that the ice streams deposited on the outer margin. Our results show that the northwestern margin of Svalbard experienced a switching of a major ice stream. Based on correlation with the regional seismic stratigraphy as well as the results from ODP 911 on Yermak Plateau and ODP 986 farther south on the western margin of Spitsbergen, off Van Mijenfjord, we find that first a northwestward flowing ice stream developed during initial northern hemispheric cooling (starting ∼2.8–2.6 Ma). A switch in ice stream flow direction to the present-day Kongsfjorden cross-shelf trough took place during a glaciation at ∼1.5 Ma or probably later during an intensive major glaciation phase known as the ‘Mid-Pleistocene Revolution’ starting at ∼1.0 Ma. The seismic and bathymetric data suggest that the switch was abrupt rather than gradual and we attribute it to the reaching of a tipping point when growth of the Svalbard ice sheet had reached a critical thickness and the ice sheet could overcome a topographic barrier.

Temperature evolution on Rh/Al 2O 3 catalyst during partial oxidation of methane in a reverse flow reactor

Catalytic partial oxidation of methane was investigated in a reverse flow reactor with commercial Rh/Al 2O 3 catalyst in pellets. The process is carried out in a catalytic fixed bed reactor and switching of feed flow direction is obtained through four electrovalves synchronized in pairs. Temperature profile along the catalyst bed was measured by fast IR thermography and product composition was measured with a continuous gas analyzer. Feed direction switching time, water to methane ratio and inert section length were investigated as process parameters. Data of catalyst bed temperature evolution during the flow cycle are presented, discussed and related to reactor performance as a function of reverse flow switching period. The effect of water addition to the reacting mixture on the dynamics of catalyst bed temperature evolution is also presented.

Pilot-Scale Compost Media Biofilter Treatment Of Volatile Organic Compounds

The compost media biofilter is one of the most important biological processes applied to treat waste gases. Research on a pilot-scale compost media biofilter treatment of volatile organic compounds (VOCs) was performed. The volume of biofilter media was 4.3 m3 and the biofilter operated for 57 days. Fluctuation of water content in the biofilter media was investigated. With continuous switching of air flow direction, the water content of the biofilter media could be managed without any addition of exterior water. The range of average temperature of each stage measured between 18°C to 73°C. When the air flow direction switched from upward to downward, temperatures of lower stages increased and temperatures of upper stages decreased. Temperatures of one side of the media were usually higher than those of the opposite side at the same depth. Compost has the advantages of different types of nutrients present in the media. With the compost media, the removal efficiency of the biofilter could be maintained at more than 99% for the experimental period.

Periodic Operation of Three — Phase Catalytic Reactors

AbstractPeriodic operation of three phase reactors has been explored for more than two decades. This type of forcing changes selectivity and can increase either conversion or throughput. Experiments and simulation demonstrate periodic flow interruption or variation enhances reaction rates for concurrent trickle beds provided reactants are in the gas phase or can be volatilized under bed operating conditions. Temperature excursions in trickle beds can be controlled by either flow variation or switching the feed between an inert and a reactant. Several approaches to increasing rate through faster mass transfer using flow pulsing have been studied. Pulsing flow can be induced by low amplitude modulation. Periodic switching of flow direction in airlift reactors increases gas hold up and thereby the mass transfer rate. Periodic operation of three phase reactors, thus, appears to be a fertile area for engineering research.

Switch of flow direction in an Antarctic ice stream.

Fast-flowing ice streams transport ice from the interior of West Antarctica to the ocean, and fluctuations in their activity control the mass balance of the ice sheet. The mass balance of the Ross Sea sector of the West Antarctic ice sheet is now positive--that is, it is growing--mainly because one of the ice streams (ice stream C) slowed down about 150 years ago. Here we present evidence from both surface measurements and remote sensing that demonstrates the highly dynamic nature of the Ross drainage system. We show that the flow in an area that once discharged into ice stream C has changed direction, now draining into the Whillans ice stream (formerly ice stream B). This switch in flow direction is a result of continuing thinning of the Whillans ice stream and recent thickening of ice stream C. Further abrupt reorganization of the activity and configuration of the ice streams over short timescales is to be expected in the future as the surface topography of the ice sheet responds to the combined effects of internal dynamics and long-term climate change. We suggest that caution is needed when using observations of short-term mass changes to draw conclusions about the large-scale mass balance of the ice sheet.

Modelling of spatiotemporal patterns in a sequence of catalytic monolith reactors

System of monolith metallic (M) and ceramic (C) catalytic reactors described by two-phase model with axial dispersion is studied for CO oxidation. Values of kinetic and transport parameters are fitted to experimental ignition data. Periodic flow reversal is shown to stabilize temperature fronts in the C-M-C and M-C-M combination of monoliths. Existence of unsymmetric spatial temperature regimes and the possibility of adaptive control of flow direction switching are demonstrated.

Influencing hollow fiber bioreactor hydrodynamics through osmotic pressures—A model study

Experiments have shown that secondary fluid flows within the extra-capillary space (ECS) of hollow fiber bioreactors (HFBRs) can lead to the downstream polarization of cells and growth factors and subsequent reductions in reactor productivity. Recent model studies and experimental investigations of this system have demonstrated further that the polarization of ECS solutes can be reduced through increased loading of bovine serum albumin within the ECS, which leads to a concomitant reduction in solute convection via osmotic pressure effects. The following study extends previous models of HFBR hydrodynamics to include the effect of multiple solute species on the transient distribution of ECS solutes. The model is then used to study the relative effectiveness of dextran 500, dextran 70, hydroxyethylstarch 120, and bovine serum albumin, as well as periodic switching of the fiber lumen flow direction, in eliminating solute polarization. The high molecular weight additives are found to be more effective than flow switching in reducing polarization, particularly when the membranes display permeabilities characteristic of some polysulfone fibers (i.e. 6 × 10 −13 m).