Measurement Of Flow Distribution Research Articles

Distribution of relaxation times: A method for measuring air flow distribution in high-temperature proton exchange membrane fuel cell stacks

Measurement of flow distribution in the fuel cell stack is a challenging task. This study proposes a new method to measure air flow distribution in high-temperature proton exchange membrane fuel cell stacks. The characteristic frequency related to channel impedance is extracted using the distribution of relaxation times analysis. A simple correlation between the air stoichiometry and the characteristic frequency is developed. The influence of various factors on the correlation, including cell operation conditions, fluid physical properties and channel dimensions, are investigated. The experimental results show a good agreement with the correlation. Error estimation indicates that the temperature distribution of the stack, gas humidity and pressure distribution in the inlet manifold have no significant effect on the proposed method under normal conditions. The accuracy and practicability are verified using a three-cell stack with separate mass flow controller (MFC) systems. The results show less than 3.11% of relative error between the reference air stoichiometry given by the MFC and those measured from our proposed method for air stoichiometry below 3.0 at 0.1 A cm−1. The present method provides powerful support for designing high consistency stacks and the real-time monitoring cells state-of-health in stacks.

Flow Distribution in U- and Z-Type Manifolds: Experimental and Numerical Investigation

Heat exchangers are used to transfer energy from one medium to another and increase contact area for higher efficiency. In case of fluids, higher flow area would lead to high/low flow zones that severely affect the fluid dynamics and thermal performance. Channels are used to distribute the flow uniformly to fully utilize the whole heat exchanger area. The flow uniformity in a flow distribution manifold is dependent on several factors such as flow rate, inlet and exit locations, and the manifold and channel geometrical configuration. In the current work, flow distribution measurements were performed using a particle image velocimetry (PIV) technique in two types of rectangular manifolds. The experimental results are further verified against the results obtained from numerical modeling with similar trends. The flow distribution in U- and Z-type arrangements are evaluated and compared with ten channels incorporated in the design. It was found that the flow is more in the channels near the inlet for U-type design, while more near the outlet for the Z-type. An increase in the inlet flow rate enhances the flow distribution for the U-type while results in more maldistribution for the Z-type. For the U-type, the normalized velocity varies from 1.34 to 0.52 in a wide manifold, and between 2.82 and 0.18 for a narrow manifold. A U-type wider manifold is recommended for all conditions examined in this work since at lower flow rates, both have similar mirrored distribution, while at higher flow rates, U-type manifold has better flow distribution.

Experimental characterization of thermal-hydraulic performance of a microchannel heat exchanger for waste heat recovery

Given size and performance advantages, microchannel heat exchangers are becoming increasingly important for various energy recovery and conversion processes. In this study, detailed experimental measurements were conducted to characterize flow and heat transfer performance of a microchannel heat recovery unit (HRU) manufactured using standard photochemical etching and diffusion bonding processes. According to the global flow and temperature measurement, the HRU has delivered the predicted thermal performance under various oil and air flow rates. As expected, the heat transfer effectiveness varies between 88% and 98% for a given air and oil flow rates while it increases with air inlet temperature due to the improved thermal conductivity. However, significant flow mal distribution is identified among the air channels according to the in-depth flow distribution measurement using hot wire. The flow measurement also indicates visible misalignment of the air channels caused by the manufacturing processes. In addition, the excessive pressure drops occurred for both air and oil channels indicating reduced flow areas due to the photochemical etching process. The results of this experimental study can hopefully provide insights in improving designs of microchannel heat exchangers using the same manufacturing processes.

In Vivo Evaluation of the Cardiovascular System of Mouse Embryo and Fetus Using High Frequency Ultrasound.

Genetically engineered mice have been widely used for studying cardiovascular development, physiology and diseases. In the past decade, high frequency ultrasound imaging technology has been significantly advanced and applied to observe the cardiovascular structure, function, and blood flow dynamics with high spatial and temporal resolution in mice. This noninvasive imaging approach has made possible longitudinal studies of the mouse embryo/fetus in utero. In this chapter, we describe detailed methods for: (1) the assessment of the structure, function, and flow dynamics of the developing heart of the mouse embryo during middle gestation (E10.5-E13.5); and (2) the measurement of flow distribution throughout the circulatory system of the mouse fetus at late gestation (E17.5). With the described protocols, we are able to illustrate the main cardiovascular structures and the corresponding functional and flow dynamic events at each stage of development, and generate baseline physiological information about the normal mouse embryo/fetus. These data will serve as the reference material for the identification of cardiovascular abnormalities in numerous mouse models with targeted genetic manipulations.

Numerical and experimental investigation on the realization of target flow distribution among parallel mini-channels

Fluid flow maldistribution is considered as one of the main causes of performance deterioration in various energy and process systems, especially when parallel micro- or mini-channel fluidic networks are involved. For a specific purpose, the optimal flow distribution is not necessarily uniform. However, specific non-uniform distributions are somewhat more difficult to achieve than uniform ones. The insertion of a geometrically optimized baffle has been numerically confirmed as an effective solution to this issue, but experimental validation is still lacking which is indispensable for bridging the gap between theory and practice.This paper presents a numerical and experimental investigation on the realization of target flow distribution among parallel mini-channels, using the optimized baffle insertion method. A 15-channel fluidic network integrated with the distributor and the collector is fabricated and tested. Various perforated baffles are optimized and fabricated corresponding to different target distributions (uniform, ascending and descending). PIV technique is used for the flow distribution measurement while CFD simulations are also performed for comparison. CFD results and PIV data show that different target distributions could be successfully achieved by the optimized baffle insertion method. The robustness of the optimized baffle for uniform distribution is also evaluated and discussed to provide some guidelines for future applications.

Experimental measurement of flow distribution in a parallel mini‐channel fluidic network using PIV technique

AbstractFluid flow distribution among parallel channels usually plays an important role on the global performance improvement of tubular process equipment, but remains difficult to be properly measured by experimental methods. This paper presents a systematic study on the measurement of flow distribution in a multi‐channel fluidic network using Particle Image Velocimetry (PIV) technique. For the precise measurement of flow‐rate in each individual channel, standard 2 dimensions, 2 components PIV technique is used to obtain velocity vectors on multiple sampling planes parallel to the flow direction, so as to reconstruct accurate velocity profiles on the cross‐sectional surface. Such procedure is repeated for every micro‐ (mini‐) channel to obtain the actual flow distribution properties in the fluidic network.Pre‐test results on a double‐channel device indicate that the maximum possible deviation of PIV measurements is 13.1% with respect to those of a flange flowmeter, implying that the PIV technique is relatively accurate and reliable. PIV results on the flow distribution in a 15‐channel fluidic network are then compared with Computational Fluid Dynamics simulation results under the same working conditions. A quite good agreement could be observed. Moreover, the locations and sizes of vortices in the distributor have a significant influence on the flow distribution. © 2016 Curtin University of Technology and John Wiley & Sons, Ltd.

Limitation of multiparticle correlations for studying the event-by-event distribution of harmonic flow in heavy-ion collisions

The sensitivity of flow harmonics from cumulants on the event-by-event flow distribution $p(v_n)$ is investigated using a simple central moment expansion approach. For narrow distribution whose width is much smaller than the mean $\sigma_n\ll < v_n >$, the difference between the first three higher-order cumulant estimates $v_n\{4\}$, $v_n\{6\}$ and $v_n\{8\}$ are not very sensitive to the shape of $p(v_n)$. For broad distribution $\sigma_n\gtrsim < v_n >$, the higher-order cumulant estimates differ from each other but may change sign and become ill-defined. This sign change arises from the choice of $p(v_n)$, without the need to invoke non-flow effects. Direct extraction of $p(v_n)$ via a data-driven unfolding method is a more preferred approach for flow distribution measurement.

Measurements of flow distribution in a thin resin layer during ultraviolet nanoimprint lithography by means of digital holographic particle-tracking velocimetry

There is an urgent need for micro- and nano-scale patterning methods with a high throughput and cost-effective process for the manufacture of devices of the next generation. Ultraviolet nanoimprint lithography (UV-NIL) represents a major breakthrough for next-generation lithography because of its higher resolution and greater simplicity compared with conventional technologies. However, transfer defects such as bubble defects or filling failures in the UV-NIL process have been problematic, because UV-NIL is a contact-type method. Therefore, it is important to elucidate the behavior of UV-curable resin flowing to permit control over defects in the duplicated pattern. In this study, we succeeded in measuring the flow distribution of a thin layer of UV-curable resin in situ during the press process of UV-NIL by means of microscale digital holographic particle-tracking velocimetry, and we clearly showed that a release agent coated onto the nanoimprint mold affects the resin flow. We believe that this study will help to provide a better understanding of the behavior of UV-NIL.

Variability of performance of wound infusion catheters

ObjectiveTo compare the distribution of flow from two commercial and one handmade multihole wound infusion catheters. Study designOpen label experimental measurement of flow distribution in a bench top apparatus of handmade (n = 10) and two commercial (n = 10 each) wound infusion catheters with 5–6″ (12–15.2 cm) long diffusion surfaces. MethodsThe distribution of 6 mL of distilled water injected at three different injection speeds (0.5, 5, and 120 minutes) through individual triangular pieces of felt cloth fitted over six contiguous regions of the diffusion surface of each catheter was measured in triplicate. ResultsThe distribution of flow through the six regions was significantly more uniform at the two faster injection speeds. Ninety two per cent of the 120 minute infusion trials resulted in one or more regions producing negligible flow (<5% of total output), and in 16% of the 120 minute trials all the flow came from just one or two regions. ConclusionsConstant-rate infusions of 3 mL hour−1 provide erratic distribution of flow from wound infusion catheters in a bench top apparatus. Commercial catheters did not outperform handmade catheters. Clinical relevanceUneven distribution of flow at low infusion speeds may contribute to inconsistent or unsatisfactory pain relief in patients treated with continuous wound infusions of local anesthetics.

Flow Distribution Measurement in Wire-nonparallel Plate Type Electrohydrodynamic Gas Pump by a Particle Image Velocimetry

2D Particle Image Velocimetry (PIV) measurements were performed in a wire-nonparallel plates type electrohydrodynamic (EHD) gas pump. The effect of electrode configuration and polarity of the active electrode on the flow pattern inside the pump was studied. One can deduce from the obtained flow patterns that the flow generated inside the EHD pump is three dimensional. The vortices formed inside the EHD gas pump have negative effect on pumping capabilities of the pump since the vortices may block and suppress the generated flow. The PIV results will be compared with a numerical modelling of the flow, based on k-E model.

The use of Constant Temperature Anemometry for permeate flow distribution measurement in a submerged hollow fibre system

This study investigates the application of the Constant Temperature Anemometry (CTA) technique to determine the flow distribution among hollow fibre bundles in a submerged membrane system. Membrane filtration was performed at constant permeate flux with five submerged hollow fibre membrane mini-bundles, representing regions of a submerged module, operating in parallel through a common suction pump. Five CTA sensors were located in a matrix above the outlets of the bundles so that the individual contributions of each bundle region to the net permeate flow could be monitored. This allowed measurement of the system response to simulated localised fouling or blocking, aeration failure and restoration of aeration. The CTA sensors were able to monitor the permeate flow distribution among the fibre bundles when mal-distribution of flow occurred in the system. Satisfactory performance of the CTA sensors was verified by comparing the amount of cake deposited on the membrane surface of the fibre bundles with the local flux behaviour. The results demonstrated the potential of using the CTA approach to characterise the cross-sectional fouling or blocking variation in a submerged hollow fibre membrane system. It is evident that this approach could be applied in other module configurations. Technical challenges to this CTA application are discussed.

Design of optimal extrusion die for a range of different materials

AbstractTHE coat‐hanger melt distributor is a device commonly used in the wire coating process. Its task is to distribute the melt around the conductor uniformly. It is quite common that materials and flow rates differ from what had been specified during the design procedure. This may lead to bad performance with materials of very different rheological properties from the design material. In this article, we present an optimal design approach to avoid this loss of performances. This approach involves coupling a three‐dimensional finite element simulation software with an optimization strategy based on a response surface method. The objective is to determine a coat‐hanger melt distributor geometry that ensures a homogeneous exit velocity distribution that will best accommodate for a different range of materials. A coat‐hanger melt distributor with a manifold of constant width is designed, and a set of flow distribution measurements is established for two different materials. The results of numerical simulation are then validated by comparison with experimental measurements. The effect of material change is also investigated. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers

Data streaming algorithms for efficient and accurate estimation of flow size distribution

Knowing the distribution of the sizes of traffic flows passing through a network link helps a network operator to characterize network resource usage, infer traffic demands, detect traffic anomalies, and accommodate new traffic demands through better traffic engineering. Previous work on estimating the flow size distribution has been focused on making inferences from sampled network traffic. Its accuracy is limited by the (typically) low sampling rate required to make the sampling operation affordable. In this paper we present a novel data streaming algorithm to provide much more accurate estimates of flow distribution, using a "lossy data structure" which consists of an array of counters fitted well into SRAM. For each incoming packet, our algorithm only needs to increment one underlying counter, making the algorithm fast enough even for 40 Gbps (OC-768) links. The data structure is lossy in the sense that sizes of multiple flows may collide into the same counter. Our algorithm uses Bayesian statistical methods such as Expectation Maximization to infer the most likely flow size distribution that results in the observed counter values after collision. Evaluations of this algorithm on large Internet traces obtained from several sources (including a tier-1 ISP) demonstrate that it has very high measurement accuracy (within 2%). Our algorithm not only dramatically improves the accuracy of flow distribution measurement, but also contributes to the field of data streaming by formalizing an existing methodology and applying it to the context of estimating the flow-distribution.

Measurement of Flow Distribution around a Bathtub Vortex.

Measurement of Flow Distribution around a Bathtub Vortex.

Visualization of turbulent motion using echo-planar imaging with a spatial tagging sequence

NMR imaging of instantaneous flow distribution has recently been presented by several authors (I-5). All of them have used echo-planar imaging (EPI) (6, 7) with flow-sensitive magnetic field gradients, thus measur ing flow velocity using the phase shift of moving spins. The ma jor advantage of this method is that any velocity component can be selectively measured by the application of a properly designed flowsensitive gradient. However, this “phase method” has the drawback that one phase image gives only one velocity component at a time. To overcome this problem and obtain all of the instantaneous velocity components simultaneously, a mu ltiple-spinecho EPI sequence has been proposed and applied to the measurement of turbulent motion in a cross-sectional p lane (5). It is well known, however, that there are two different approaches to NMR flow measurements: phase and amp litude methods. The phase method makes use of the phase shift of a transverse magnetization of nuclear spins moving along a magnetic field gradient. The amp litude method, on the other hand, utilizes the amp litude of a longitudinal magnetization of nuclear spins moving during a delay time. In the present study a new approach to instantaneous flow-distribution measurement categorized into the amp litude method is proposed. This method is based on a combination of EPI and a spatial tagging sequence (8-11). This technique has been applied to turbulent flows in a circular pipe. The NMR images obtained have successfully visualized the instantaneous complex fluid motions in a cross-sectional p lane perpendicular to the pipe axis. F igure 1 shows the pulse sequence used in this study. One spatial tagging process is a combination of a pulsed magnetic field gradient and nine short radiofrequency pulses whose envelope forms a sine x truncated at x = ?27r. This pulse train is a mod ification of the DANTE pulse train (11-13), producing an equally spaced stripe pattern over the object. The whole spatial tagging sequence giving a grid pattern consists of two of the spatial tagging process in which the magnetic held gradients are applied orthogonal to each other in the imaging plane. After a delay time, an image is taken with the echo-planar imaging sequence. This sequence is designed to be insensitive to a constant velocity at the first gradient echo. Thus, if the flow-associated phase shift is negligible during the data-acquisition period, the first gradient echo and the following 32 echoes can give a 64 X 64-pixel image. This is because the well-known Hermitian symmetry of the acquired NMR signal can

Instantaneous flow-distribution measurements of the equilibrium turbulent region in a circular pipe using ultrafast NMR imaging.

A powerful flow visualization and measurement method has been developed using ultrafast NMR imaging. This technique enables one to measure instantaneous distribution of any velocity component in any cross-sectional plane. This method was applied to the equilibrium turbulent region, or ``puff,'' which is intermittently created by large disturbances in a circular pipe when the Reynolds number is around 2250. Instantaneous velocity component distributions were visualized and measured for two velocity components. The flow component parallel to the pipe axis clearly demonstrated the gross nature of the equilibrium puff and that perpendicular to the pipe axis visualized the detailed structures of vortices. Longitudinal vortices were clearly observed near the pipe wall at the upstream interface as well as around the pipe axis in the downstream region. The present measurements made for a single puff, in principle, agree with the ensemble-averaged results obtained in hot-wire measurements previously reported, both qualitatively and quantitatively.

Heater probe technique to measure flow maldistribution in large scale trickle bed reactors

Novel flow distribution measurement probes were used in a large-scale commercially operating trickle-bed reactor. The probes consist of long heated pipes designed to measure local heat transfer coefficients at multiple points along their length. Local flow rates are correlated with the heat transfer coefficient based on independent laboratory data. The results of our study showed significant point-to-point variation in flow distribution. The pattern of maldistribution would vary with alternate operating conditions of flow rates, temperature, and liquid volatility. Results included an increase in the nonuniformity of flow moving down the reactor in the direction of flow. And severe maldistribution with poor reactor performance occurred at high liquid mass flux.

The effect of surface cooling on blood flow distribution in infant pigs with mature left to right shunts

Surface cooling as an adjunct to cardiopulmonary bypass, core cooling, and circulatory arrest has been effectively used to produce more homogeneous cooling and better tissue preservation. A previous study, using pigs with newly created aortopulmonary shunts, revealed a redistribution of blood flow away from the kidneys and viscera during surface cooling that did not occur in normal pigs. The present study tests the hypothesis that pigs with mature aortopulmonary shunts behave in a similar manner. Group I ( N = 7, unshunted pigs) and Group II ( N = 7, shunted pigs) underwent surface cooling and blood flow distribution measurements by microspheres at 37, 32, 28, and 25 °C. Both Groups I and II experienced a decrease in cardiac output with hypothermia. Group II had decreased absolute tissue flow to the viscera, kidneys, muscle, and skin at 37 °C compared with Group I, even before the onset of hypothermia. During hypothermia. Group I experienced a decrease in all tissue flows, but Group II had a decrease only in visceral and renal flows at 25 °C. Blood flow distribution, as a percentage of cardiac output, showed little change (decrease only in skin) in Group I with hypothermia. In Group II, however, a maldistribution of cardiac output developed resulting in decreased percentage of cardiac output to the kidneys and viscera and an increased percentage of cardiac output to the lungs that was confirmed by an increase in the Q p Q s ratio. Surface cooling in immature pigs with mature left-to-right shunts causes a maldistribution of cardiac output resulting in a decreased percentage of cardiac output to the viscera and kidneys and an increased percentage of cardiac output to the lungs. Systemic vascular resistance seems to rise to a greater degree than pulmonary vascular resistance during hypothermia and results in an increased left-to-right shunt (when present) and a maldistribution of blood flow.

Mechanisms of temperature regulation in heat-acclimated hamsters

Mechanisms of temperature regulation were assessed by measurements of oxygen consumption (VO2), body temperature (Rre = rectal, Tsk = skin), evaporative water loss (EWL), regional distribution of blood flow, and blood volume. Hamsters (Mesocricetus auratus) were acclimated to ambient temperatures of 34 or 22 degrees C. VO2 of 34 degrees C-exposed animals was reduced to 50% of that of controls at 22 degrees C, whereas EWL with heat exposure was almost double that of controls. Heat-acclimated animals had a slightly elevated Tre in comparison to 22 degrees C-acclimated animals, whereas there was a marked elevation in Tsk with heat exposure, in contrast to control animals at 22 degrees C. Blood flow distribution measurements indicated that with 34 degrees C exposure there was a decreased flow in liver, kidney, and intestine, whereas there was an increase to the carcass. Red cell and plasma volumes in heat-acclimated hamsters were decreased belwo the values of the 22 degrees C controls. Heat acclimation of the fhamster appears to involve reduced VO2 and increased WEL. Convective and radiative heat loss appear to be maintained by increased Tsk with heat exposure. Nonevaporative heat dissipation mechanisms are of primary importance in thermoregulation of the heat-acclimated hamster, and it is suggested that this is mediated by increased peripheral blood flow with reduced flow to the viscera.