Maximum Net Flow Research Articles

Computational analysis of a four-flap valveless micropump (FFVM) for low reynolds number applications in microfluidic systems

Microfluidic systems are crucial in various fields including biological fluid handling and microelectronic cooling. Micropumps play a vital role in microfluidics. Valveless micropumps are the preferred choice in microfluidics because of their ability to minimize the risk of clogging and gently handle biological materials. In this comprehensive Four-Flap Valveless Micropump (FFVM) simulation, the fluid flow and associated deformation in the valveless micropump are analyzed. The oscillatory fluid motion generated by a straightforward reciprocating pumping mechanism is transformed into a unidirectional net flow by the micropump. This pump eliminates the need for intricate actuation mechanisms found in valve-based pumps while offering precise direction control. The input is given in terms of the Reynolds number or inflow velocity. In this study, the Reynolds numbers were changed from 16 to 50, which resulted in a positive correlation with the net flow rates, yielding a maximum net flow rate of 20.81 μl min−1 at a Reynolds number of 50. The influence of the average flow velocity is evident, with a peak net flow rate of 29.16 μl min−1 at 50 cm s−1. The FFVM showcases adaptability by delivering fluid within microfluidic pathways, holding promising applications in precision drug delivery systems.

Flow Rate Augmentation of Valveless Pumping via a Time-Dependent Stenosis: A Novel Device

A novel device of flow rate augmentation is proposed and experimentally examined in a horizontal valveless closed loop pump using a time-dependent stenosis (convergent–divergent channel) in contrast with the commonly used taper tubes of constant opening as flow rectifiers. The stenosis, being a part of the flexible tube of the pump, is formed by a semi-cylindrical surface attached to a compression spring of adjustable pretension compressing the tube against a flat plate. Located at either side of the pump pincher, the shape of the stenosis changes in time, without any external power source, as a function of the fluid pressure and the pretension of the spring. The spring pretension is adjusted by a trial-and-error procedure aiming for net flow rate maximization for each pinching frequency. For the examined pitching frequencies (5 Hz to 11 Hz, for which net flow rate is maximized) and for compression ratios 38% to 75%, the maximum net flow rate was found to be 720% of the non-stenosis case. Important parameters for flow enhancement were found to be the stenosis location along the loop, its opening, the compression ratio at the pincher area and the pinching frequency.

Inhomogeneous steady shear dynamics of a three-body colloidal gel former.

We investigate the stationary flow of a colloidal gel under an inhomogeneous external shear force using adaptive Brownian dynamics simulations. The interparticle forces are derived from the Stillinger-Weber potential, where the three-body term is tuned to enable network formation and gelation in equilibrium. When subjected to the shear force field, the system develops remarkable modulations in the one-body density profile. Depending on the shear magnitude, particles accumulate either in quiescent regions or in the vicinity of maximum net flow, and we deduce this strong non-equilibrium response to be characteristic of the gel state. Studying the components of the internal force parallel and perpendicular to the flow direction reveals that the emerging flow and structure of the stationary state are driven by significant viscous and structural superadiabatic forces. Thereby, the magnitude and nature of the observed non-equilibrium phenomena differ from the corresponding behavior of simple fluids. We demonstrate that a simple power functional theory reproduces accurately the viscous force profile, giving a rationale of the complex dynamical behavior of the system.

Patterned convection in inclined slots

An analysis of laminar natural convection in inclined slots subjected to patterned heating has been performed. The imposed heating takes a simple form characterized by a single Fourier mode combined with uniform heating. It is shown that periodic heating applied at the lower plate produces no net flow when the slot is either horizontal or vertical, but a net upward flow is generated when the slot is tilted. Periodic heating applied at the upper plate produces net downward flow in the inclined situation. The addition of uniform heating promotes the upward flow while cooling has the opposite effect. There is a critical inclination angle at which the maximum net flow rate is greatest. Dynamic and thermal boundary layers are present when the wavenumber of the imposed heating is large. The use of heating at both plates, with the same wavenumber, leads to a flow dominated by the plate exposed to a more intense heating; when the two plates are heated equally no net flow is observed irrespective of the inclination angle. Changes of the relative positions of the two patterns can change the net flow rate by up to 50 %. The intensity of the flow increases with reduction of the Prandtl number. If the heating applied to the plates is of different wavelength, but of the same intensity, a wide range of behaviours of the flow system is possible. The details of this response are sensitive to the ratio of the two wavenumbers.

System modeling and characterization of enhanced valveless micropumps

This article provides a comprehensive analytical and numerical modeling procedure for characterizing the dynamics of flow fields in both the traditional circular and the new, efficiency- enhanced chambers of valveless micropump systems. The flow dynamics of the traditional circular valveless micropump system are analytically modeled and experimentally verified by comparing the results with data measured directly from a real-world system that has been discussed in the literature. The validated comprehensive modeling procedure is then extended to model the efficiency- enhanced micropump system in order to increase net flow rate and expanding the operational working range of the back pressure for possible micro devices aimed at applications for many high-performance industrial applications. A comparison of the associated system frequencies in both micropump systems shows, that the resonance frequency of the efficiency- enhanced micropump system is increased from 31 Hz to 38 Hz. The maximum net flow rate of the new system is also increased dramatically to a level of 1.74 ml/min, which is approximately 50% higher than that of the conventional setup. As long as the same input driving power is applied to both systems, the overall operating efficiency of the proposed micropump system is increased by approximately 58%. Meanwhile, the best- efficiency point (BEP) is stepped up from 0.56 ml/min to 1.1 ml/min. The enhancement of the BEP thus makes it possible for the back pressure to be operate more effectively in the range of 64 ∼ 100 Pa.

A novel valve-less piezoelectric micropump generating recirculating flow

ABSTRACT Microfluidic devices or systems to generate recirculating flow are increasingly utilized in the fields of chemistry, biomedicine, biology, with bottlenecks in integration and miniaturization needed a breakthrough. Here, a concept for a highly integrated valve-less piezoelectric micropump generating recirculating flow (VPMGRF) is proposed, simultaneously realizing innovation in theory and method. Based on fluid inertiaand energy dissipation of vortexes, a novel double-loop tube was designed to achieve fluid flow in different directions along various paths, with the flow characteristics at different cross-sectional areas explored through computational fluid dynamics (CFD). Afterwards, as valve bodies, the double-loop tubes were connected with a piezoelectric-actuated chamber to constitute the VPMGRF, which was followed by establishing a theoretical model of the vibration, fluid dynamics, and net flow rate. Eventually, experimental results showed that VPMGRFs could generate internal recirculating flow and had a pump effect. The maximum net flow rate reached 5.19 mL/min at 8 Hz, corresponding to a vibrator amplitude of 35 μm and an output pressure amplitude of 4.27 kPa. Furthermore, the larger the characteristic length of the cross section, the greater the amplitude of the vibrators, the larger the amplitude of output pressure, and the slower the flow rate.

A novel valveless piezoelectric micropump with a bluff-body based on Coanda effect

Based on the Coanda effect, a novel valveless micropump is presented in this paper, the special bluff-body is utilized to enhance the Coanda effect and increase the net flow of the micropump. In order to reveal the influence of structural parameters on the performance of novel micropump, five micropump samples with different chamber radii (5 mm and 9 mm), aspect ratios (4 and 8) and channel angles (30° and 45°) are fabricated by silicon-based MEMS technology. On the conditions of the voltages (50–300 vpp) and excitation frequencies (25–125 Hz), the performance of the micropumps is studied experimentally in detail. As the voltage V = 300 vpp and the frequency f = 50 Hz, the maximum net flow and back pressure for the optimal sample can attain 4.84 ml/min and 1.75 kPa, respectively. Through numerical simulations, the efficiency of the micropumps with different aspect ratios L1/d (3–9) are investigated as Reynolds number range from 300 to 1000 at the frequencies of 5–400 Hz. When the Reynolds number is constant, the pump efficiency has the optimal value with the increase of frequency, and the streamline diagrams indicate that this is related to the effects of the internal vortexes.

Mixed-Integer Programming for Cycle Detection in Nonreversible Markov Processes

In this paper, we present a new, optimization-based method to exhibit cyclic behavior in nonreversible stochastic processes. While our method is general, it is strongly motivated by discrete simulations of ordinary differential equations representing nonreversible biological processes, in particular, molecular simulations. Here, the discrete time steps of the simulation are often very small compared to the time scale of interest, i.e., of the whole process. In this setting, the detection of a global cyclic behavior of the process becomes difficult because transitions between individual states may appear almost reversible on the small time scale of the simulation. We address this difficulty using a mixed-integer programming model that allows us to compute a cycle of clusters with maximum net flow, i.e., large forward and small backward probability. For a synthetic genetic regulatory network consisting of a ring oscillator with three genes, we show that this approach can detect cycles that have a productivi...

Diagnosis of oscillating pressure-driven flow in a microdiffuser using micro-PIV

In this study, the characteristics of oscillating pressure-driven flow in a microdiffuser are examined by μPIV (micro Particle Image Velocimetry) diagnostics. Utilizing a cam-follower system, a dynamic pressure generator is built in-house to provide a time-varying sinusoidal pressure source. Three parameters are examined experimentally: the excitation frequency, the cam size, and the half-angle of the microdiffuser. Driven by oscillating pressure, we find that there exists an optimal half-angle such that maximum net flow is attained in the expansion direction. Contrarily to the prediction of hydraulics theory which only considers steady flow, flow in the microdiffuser of the optimal half-angle does not necessarily remain attached. Rather, maximum net flow can also occur in microdiffusers where vortices retain a slender shape. When vortex bubbles are slender, the μPIV results reveal that the core flow accelerates to a higher forward velocity during the first half of the cycle and flow rectification is actually enhanced. Due to the three-dimensional flow structure, fluid is drawn out of the vortices near the reattachment point to join the core flow and consequently magnifies the forward flow. As the half-angle increases, vortices become rounder and the core flow is drastically narrowed to reduce flow rectification.

Dead-end ultrafiltration in hollow fiber modules: Module design and process simulation

Ultrafiltration in a hollow-fiber module operating with outside-in and dead-end flow at a constant flow rate was simulated using a model that takes into account the longitudinal pressure drops inside the fibers and within the fiber bundle. The model considers both the filtration phase during which the membrane is fouled by the formation of a filter cake and the backwash phase in which it is cleaned, so as to predict the net rate of production of the module during an operating cycle. The results show that there is a combination of packing density and fiber diameter that gives a maximum net flow rate. Furthermore, this model allows the influence of operating conditions and feed properties on the module performance to be estimated. This can be used to determine how operating parameters must be modified when there is a change in the feed properties.

Convective fluid flow through the paracellular system of Necturus gall-bladder epithelium as revealed by dextran probes.

1. Bidirectional paracellular fluxes using radioactive dextrans as inert molecular probes have been measured across Necturus gall-bladder epithelium during conditions of normal fluid absorption. There is a net flux at all radii analysed (0.4-2.2 nm) in the direction of fluid absorption. 2. The net flux is substantial at all radii within the range. The data extraplate to 2 x 10(-6) cm s-1 at zero probe radius, which is very close to the rate of epithelial fluid absorption. 3. The unstirred layers at the epithelial faces during transport have been determined; their contribution to the net fluxes is negligible. 4. Two possible mechanisms for the net flow of probes are considered: (i) that the probes diffuse across the junctions and are then entrained in a local osmotic flow along the interspaces and subepithelium; (ii) that the probes are entrained in volume flow across the junctions and the emergent solution subsequently passes through the interspaces and subepithelium. Model calculations clearly rule out mechanism (i) in which the maximum net flow obtainable is less than 10% of that observed. In addition the presence of leak paths shunting the junctions is not compatible with the observed fluxes. With mechanism (ii) the net flows are correctly predicted with all the fluid flow being transjunctional. The fluid absorption is therefore entirely paracellular. 5. The slope of the net flow curve shows no apparent change in magnitude over the range of the probe radii, indicating that effectively only one population of convective channels is present with parallel walls separated by about 7.7 nm. This agrees with the width previously determined by electron microscopy. 6. If the fluid absorption is junctional then the cellular route offers little if any relative contribution. The hydraulic conductivity of the junctions is not high enough, or the osmotic permeability of the membranes low enough, to accommodate this by osmosis and therefore the junctional fluid absorption must be non-osmotic.

Storage requirements for water in the United States

Storage requirements for various levels of streamflow regulation in the 22 major regions of the contiguous United States are presented to supersede those given in Committee Print 32 of the Select Committee on National Water Resources, U. S. Senate. At high levels of development, the storage required to provide the desired flow in 95 and 98% of the years is substantially larger than that previously given. Carry‐over storage requirements based on probability routing of annual discharge are combined with seasonal storage requirements to give the revised storage requirements, which are then used to compute revised evaporation losses and revised cost estimates by the methods previously used. The maximum net flow that could be made available for the 22 regions for 98% of the years is shown to be 965 billion gallons per day (bgd) for which a storage capacity of 3.6 billion acre‐feet would be required. A net flow of 922 bgd could be made available with 2 billion acre‐feet of storage. Any increment of flow above the 922 bgd figure would have storage costs exceeding 10 cents per thousand gallons delivered.