Low Flow Rate Regime Research Articles

Holographic PIV/PTV for nano flow rates-A study in the 70 to 200nL/min range.

Accurately measuring flow rates is a key requirement in many medical applications such as infusion and drug delivery systems. A major drawback of current systems is the low resolution of the sensors in the low flow rate regime. In this article, we present a method based on Holographic PIV/PTV that has been used for the first time to measure flow rates in the range of a few nL/min. Our method requires a very simple setup that combines lensless holography with particle velocimetry. For flow rates in the 70 to 200nL/min range, the highest uncertainty was 5.6% (coverage factor k=2). This is an open-source project; the CAD designs and software source code are available at https://github.com/gui-miotto/holovel.

Oscillation characteristics of mutually impinging dual jets in a mixing chamber

In this study, we consider the oscillatory behavior of mutually impinging jets in an enclosed, dome-shaped mixing chamber. The frequency of the impinging jet oscillations is dictated by the flow rate, with the oscillatory behavior being grouped into three regimes: a low flow rate regime (Re < 1500), a transition regime (1500 < Re < 2000), and a high flow rate regime (Re > 2000). The detailed characteristics of the oscillations in the high flow rate regime (Re = 6800 in the present study) are investigated through simultaneous frequency and refractive-index-matched particle image velocimetry measurements. The oscillation mechanism in the high flow rate regime was found to be similar to that of the other two regimes, where jets collide and interact in an oscillatory manner. However, in the high flow rate regime, there is a distinct and phase-evolving process of saddle point formation and jet bifurcation that is not present at the lower flow rates. The jet bifurcation process is also distinctly related to the balance of vortical structures inside the mixing chamber, and saddle point formation plays a key role in the internal and external flow field of this configuration. The external sweep angle of the exiting jet increases with the flow rate throughout the low and transition flow rate regimes, but a constant sweep angle was found to persist in the high flow rate regime. Thus, formation and location of the internal saddle point is directly linked to the external sweep angle of the jet.

Hybrid integration of scalable mechanical and magnetophoretic focusing for magnetic flow cytometry

Time-of-flight (TOF) magnetic sensing of rolling immunomagnetically-labeled cells offers great potential for single cell function analysis at the bedside in even optically opaque media, such as whole blood. However, due to the spatial resolution of the sensor and the low flow rate regime required to observe the behavior of rolling cells, the concentration range of such a workflow is limited. Potential clinical applications, such as testing of leukocyte function, require a cytometer which can cover a cell concentration range of several orders of magnitude. This is a challenging task for an integrated dilution-free workflow, as for high cell concentrations coincidences need to be avoided, while for low cell concentrations sufficient statistics should be provided in a reasonable time-to-result. Here, we extend the spatial bandwidth of a magnetoresistive sensor with an adaptive and integratable workflow concept combining mechanical and magnetophoretic guiding of magnetically labeled targets for in-situ enrichment over a dynamic concentration range of 3 orders of magnitude. We achieve hybrid integration of the enrichment strategy in a cartridge mold and a giant-magnetoresistance (GMR) sensor in a functionalized Quad Flat No-Lead (QFN) package, which allows for miniaturization of the Si footprint for potential low-cost bedside testing. The enrichment results demonstrate that TOF magnetic flow cytometry with adaptive particle focusing can match the clinical requirements for a point-of-care (POC) cytometer and can potentially be of interest for other sheath-less methodologies requiring workflow integration.

Numerical evaluation of SmCo permanent magnet flowmeter measuring sodium flow in a low flow rate regime using FLUENT/MHD module

One of the several key subsystems in the test facility of Korean sodium-cooled fast reactor is a plugging meter system, which measures the impurities in the sodium using an indirect online technique. To measure the low flow rate, a permanent magnet flowmeter was developed owing to its inherent fast response time, non-invasive characteristic, relatively accurate flow rate measurements, and excellent linearity between the flow rate and flowmeter signal. However, several limitations have been reported in the experimental evaluation of the flowmeter under low flow rate conditions given the measurement capability of the current experimental facility. Thus, the performance of the flowmeter was evaluated numerically using a commercial computational fluid dynamics tool, a FLUENT/MHD module, based on the finite volume method with the help of electromagnetic analysis software, ANSYS MAXWELL. The FLUENT/MHD module was validated by comparing the simulation results with the experimental results. The relative error of the FLUENT simulation was estimated to be approximately 0.24% compared with the experimental results. After the validation process, MHD simulations were conducted to calculate the flowmeter voltage signals versus flow rates, especially in a low flow rate regime, where the linearity between the flow rate and flowmeter signal was carefully analyzed.

Effective rheology of Bingham fluids in a rough channel

We derive the volumetric flow rate versus pressure drop of a Bingham fluid in one-dimensional channels of variable apertures in the lubrication approximation. A characteristic length scale, $a^*$ characterizing the flowis introduced in order to distinguish between a high and a low flow rate regime. We illustrate the calculation for channels with periodically varying apertures. We then go on to consider apertures that are self affine. We determine how the scaling properties of the aperture field is reflectedin the effective flow equations.Finally, a series expansion for high and low flow rates that works very well over the entire range of flow rates is proposed.This truncated expansion allows us to predict the domain of validity of the two expansions by comparing $a^*$ to the aperture distribution.

Realizing nano electrospray ionization using disposable pipette tips under super atmospheric pressure

Nano electrospray with a solution flow rate below 100 nL min(-1) is usually performed using a metallized pulled glass capillary with an inner diameter tip of <10 μm. In this paper, we demonstrated that it was possible to achieve a stable solution flow rate of ~10 nL min(-1) for an aqueous solution using a disposable plastic pipette tip with an inner diameter of 100 μm as an ESI emitter. This pipette tip (gel loading tip) was originally designed for the loading of sample onto the gel in gel electrophoresis. The inner and outer diameters were much larger than those of a nanoESI emitter, but the low solution flow rate could be sustained by conducting the electrospray under a super-atmospheric gas pressure. The high pressure condition ensured the absence of electrical discharge which was essential for stable electrospray of aqueous solution. ESI with this low cost tip was equally as sensitive as the standard nanoESI emitter and capable of producing a long lasting signal from a small amount of sample liquid. Due to a small initial droplet size under the low flow rate regime, ESI with the present method exhibited the property of nanoESI where the ion suppression of the hydrophilic analyte by the hydrophobic compound present in the solution was greatly reduced. Furthermore, owing to its larger inner diameter, the tip relatively easily avoided the clogging problem often encountered when dealing with "dirty" samples when compared with a nanoESI emitter made from a fine glass capillary.

Light sheet based imaging flow cytometry on a microfluidic platform

ABSTRACTWe propose a light sheet based imaging flow cytometry technique for simultaneous counting and imaging of cells on a microfluidic platform. Light sheet covers the entire microfluidic channel and thus omits the necessity of flow focusing and point scanning based technology. Another advantage lies in the orthogonal detection geometry that totally cuts‐off the incident light, thereby substantially reducing the background in the detection. Compared to the existing state‐of‐art techniques the proposed technique shows marked improvement. Using fluorescently‐coated Saccharomyces cerevisiae cells we have recorded cell counting with throughput as high as 2,090 cells/min in the low flow rate regime and were able to image the individual cells on‐the‐go. Overall, the proposed system is cost‐effective and simple in channel geometry with the advantage of efficient counting in operational regime of low laminar flow. This technique may advance the emerging field of microfluidic based cytometry for applications in nanomedicine and point of care diagnostics. Microsc. Res. Tech. 76:1101–1107, 2013. © 2013 Wiley Periodicals, Inc.

Heat Transfer Augmentation: Radiative-Convective Heat Transfer in a Tube With Fiber Array Inserts

Gas-phase heat transfer plays a critical role in many high temperature applications, such as preheaters, combustors, and other thermal equipment. In such cases common heat transfer augmentation methods rely on the convective component alone to achieve improved internal performance. Radiatively assisted heat transfer augmentation has been suggested as a way to overcome limitations in convective-only enhancement. One example of such a technique is the fiber array insert; thermal radiation emitted by tube walls is captured by a large number of slender fibers, which in turn convect heat to the flowing fluid. Previous numerical studies have indicated that this technique represents a promising enhancement method warranting further investigation. This paper presents results from an experimentally based feasibility study of fiber array inserts for heat transfer augmentation in an externally heated duct. Fibers composed of 140 μm silicon carbide and 150 μm stainless steel were assembled in arrays with porosities around 0.98, and were tested for empty-tube Reynolds numbers ranging from 17,500 to 112,500 and wall temperatures from ambient up to 750°C. The arrays cause a significant pressure drop—roughly two orders of magnitude higher than the empty-tube case—but tube-side heat transfer coefficients were improved by up to 100% over the convective-only case in the low flow rate regime. The stainless steel fiber array exhibited similar heat transfer performance as the silicon carbide case, although pressure drop characteristics differed owing to variations in fluid-structure flow phenomena. Pressure drop data were roughly within the range of d’Arcy law predictions for both arrays, and deviations could be explained by inhomogeneities in fiber-to-fiber spacing. Heat transfer was found to depend nonlinearly on wall temperature and flow rate, in contrast to previously reported numerical data.

Two-Phase Flow Pressure Drop Characteristics in Trapezoidal Silicon Microchannels

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper focuses on experimentally studying the pressure drop characteristics for two-phase flow in microchannels of hydraulic diameter 109 <formula formulatype="inline"><tex Notation="TeX">$\mu {\rm m}$</tex> </formula>, over a relatively large range of heat flux of (0–30 <formula formulatype="inline"><tex Notation="TeX">${\rm W}/{\rm cm}^{2}$</tex></formula>) and mass flow rate values (44–1114 <formula formulatype="inline"><tex Notation="TeX">${\rm kg}/{\rm m}^{2}\hbox{-}{\rm s}$</tex></formula>). Three fluid flow regimes (single-phase, two-phase, and dryout) have been covered in this paper, with deionized water as the working fluid. For a given heat flux, the variation of average pressure drop with flow rate can be classified into three distinct regimes. In the first regime (higher flow rate), the pressure drop decreases linearly with decrease in flow rate. In the second regime (lower flow rate), pressure drop increases with decreasing flow rate and reaches a maximum (with a minimum on either side). Finally, in the very low flow rate regime, pressure drop increases rapidly with decreasing flow rate. The average pressure drop in the two-phase regime is predicted well by the annular flow model. In addition to absolute pressure drop values, we also report pressure fluctuations. The magnitude of pressure fluctuations appears to be correlated to the underlying flow regime, such as bubbly, slug, and annular regimes, which have been identified through the flow visualization. An important outcome of this study is the identification of as many as four operating points with similar pressure drop penalty. This may help to choose the right operating conditions for a microchannel-based heat sink for use in cooling electronics. These detailed experimental results are also expected to be useful for modeling two-phase flow in microchannels. </para>

An approximate method for calculating laminar natural convective motion in a trombe-wall channel

Laminar natural convective motion in a channel formed by differentially heated vertical plates is analyzed. The proposed model combines the momentum-integral equation with the Oseen approximation for convective terms in the energy equation to predict the volumetric flow rate as a function of channel height. A second-order ordinary differential equation for pressure defect in the channel is derived by approximating the axial velocity profile with a fourth-order polynomial. Results obtained from the present model are in good agreement with previously reported results. Consideration of a second-order axial velocity profile in the momentum-integral model leads to closed form solutions that are in good agreement with previously reported results only in the mid to high flowrate regime. In the low flow-rate regime, the second-order model gives results that deviate significantly from results obtained for other models. Neglect of inertia terms in the momentum-integral model leads to a first-order differential equation for the pressure and a closed form solution of the problem. However, this approximation yields results that are good only in the mid to high flowrate regime, while showing deviations from other models in the low flowrate regime. Finally, the present model is also shown to be capable of application to fluids with widely ranging Prandtl numbers.

Distribution of blood flow in vascular beds: model study of geometrical, rheological and hydrodynamical effects.

The problem of regional blood flow distribution in small vessels is considered by means of a passive model of a portion of the vascular bed. The following complexities are considered: (1) non-Newtonian behavior of blood including effects of red cell aggregation, (2) the complexity of the vascular g eometry including taper, curvature and effects at bifurcations, and (3) flow unsteadiness. Three rheological models are considered, namely Newtonian, power-law and Casson fluids. It is shown that changes in flow distribution and even reversal of flow direction can occur if the fluid is non-Newtonian but not a power-law fluid. It is shown that this condition is satisfied for blood in the low flow-rate regime where erythrocyte aggregation is important. Computations indicate that local pressure changes due to inertial effects as a result of vessel non-uniformity are not important. It is suggested that alterations in blood flow distribution due to rheological changes will show up experimentally in measurements of ventilation-perfusion relationships in the lung or in analysis of in vivo dye-dilution curves.