Thin Rectangular Channel Research Articles

A rheophysical study of the non-newtonian behavior of water flow in thin channels

The development of low-permeable hydrocarbon reservoirs is becoming an increasingly urgent task, and therefore, the study of the laws of fluid movement in subcapillary pores and microcracks is a crucial scientific and technical problem. The previous experimental studies revealed that a viscous liquid during flow in low-permeable reservoirs exhibits an anomalous non-Newtonian character, accompanied by a violation of the linearity of the filtration process, and, consequently, Darcy's law. It was also established that starting from a certain critical size of the opening of the crack, the flow of a Newtonian fluid (water, viscous oil) becomes non-Newtonian, with the manifestation of an initial pressure gradient and flow locking. In this research work, rheophysical aspects of the non-Newtonian behavior of water during flow in thin rectangular channels are considered experimentally. Using the microchannel model, it is established that the nonlinear rheological effect in the flow of water in micro-slits is mainly caused by the value of the electrokinetic potential of the system, by reducing of which it is possible to significantly weaken the non-Newtonian nature of the fluid. To regulate the electrokinetic potential of the fluid system, an antistatic additive was used, the optimal concentration of which was established experimentally. The optimal concentration is defined to be 0.006 %. Based on the Bingham model, the rheological parameters of water flow were estimated at different micro-slit clearances changed in the range of 10÷25 micrometers, in the absence and presence of an antistatic additive. It is also established that a reduction in the electrical potential of the fluid flow leads to a significant decrease in the yield shear stress during the flow of water in the microchannel

Hydrodynamic irreversibility of non-Brownian suspensions in highly confined duct flow

The irreversible behaviour of a highly confined non-Brownian suspension of spherical particles at low Reynolds number in a Newtonian fluid is studied experimentally and numerically. In the experiment, the suspension is confined in a thin rectangular channel that prevents complete particle overlap in the narrow dimension and is subjected to an oscillatory pressure-driven flow. In the small cross-sectional dimension, particles rapidly separate to the walls, whereas in the large dimension, features reminiscent of shear-induced migration in bulk suspensions are recovered. Furthermore, as a consequence of the channel geometry and the development and application of a single-camera particle tracking method, three-dimensional particle trajectories are obtained that allow us to directly associate relative particle proximity with the observed migration. Companion simulations of a steadily flowing suspension highly confined between parallel plates are conducted using the force coupling method, which also show rapid migration to the walls as well as other salient features observed in the experiment. While we consider relatively low volume fractions compared to most prior work in the area, we nevertheless observe significant and rapid migration, which we attribute to the high degree of confinement.

Current reversal in polar flock at order-disorder interface.

We studied a system of polar self-propelled particles (SPPs) on a thin rectangular channel designed into three regions of order-disorder-order. The division of the three regions is made on the basis of the noise SPPs experience in the respective regions. The noise in the two wide regions is chosen lower than the critical noise of order-disorder transition and noise in the middle region or interface is higher than the critical noise. This makes the geometry of the system analogous to the Josephson junction (JJ) in solid-state physics. Keeping all other parameters fixed, we study the properties of the moving SPPs in the bulk as well as along the interface for different widths of the junction. On increasing interface width, the system shows an order-to-disorder transition from coherent moving SPPs in the whole system to the interrupted current for large interface width. Surprisingly, inside the interface, we observed the current reversal for intermediate widths of the interface. Such current reversal is due to the strong randomness present inside the interface, which makes the wall of the interface reflecting. Hence, our study gives new interesting collective properties of SPPs at the interface which can be useful to design switching devices using active agents.

Removal of Iron Carbide in Turbulent Flow Conditions and Influence of Iron Carbonate Formation in Aqueous CO2 Corrosion of Mild Steel

Iron carbide or cementite (Fe3C) is often classified as a “corrosion product” but it is originally found in the material’s microstructure and, unlike iron carbonate (FeCO3), it is not precipitated on the steel surface. Rather, it represents the leftover steel structure once the ferrite phase has corroded away. Various researchers have found that Fe3C acts as a diffusion barrier between iron and carbonate ions, which aids in the precipitation of FeCO3. Previous studies have also considered various material compositions and microstructures favoring FeCO3 formation. However, the effect of flow has not been considered previously although it plays a critical role in Fe3C adherence to the steel surface as it is a fragile leftover layer. In this study, a ferritic-pearlitic UNS G10180 material was exposed to flow velocities (0.4 m/s, 2 m/s, and 6 m/s) and shear stresses (0.8 Pa, 20 Pa, and 100 Pa) in a thin rectangular flow channel at favorable layer formation conditions (T = 80°C, pH 6.6, initial [Fe2+] = 2 ppm, initial S(FeCO3) ≈ 10). A critical velocity for Fe3C removal was identified, which further prevented the formation of FeCO3, although it is fully expected that its value should depend on the operating conditions.

Influence of low-frequency vibrations on mass transfer in pores

The work is devoted to the numerical investigation of mass transfer in a narrow extended channel at small low-frequency fluid vibrations. These questions are of interest for technological processes associated with impregnation and filtration. Three different series of mass transfer problems are considered. In the first series a low velocity flow with some diffusing component was supplied through the initial section of a long thin rectangular channel. In the second series the speed fluctuation near the zero point was considered, i.e. there was no stationary component of the fluid velocity in the channel. In the third series of calculations the mass transfer was determined for the case when the dissolving substance was absorbed on the opposite wall of the channel. Calculations of mass transfer in capillary channels showed that with longitudinal oscillations of the flow in the channel, the amplitude of the velocity oscillations has the main influence while the frequencies play practically no role.

FIRST STEPS TO COUPLED HYDRAULIC AND MECHANICAL CALCULATIONS WITHIN A PARAMETER STUDY TO DEFINE POSSIBLE CORE DESIGNS FOR THE CONVERSION OF FRM II

The Forschungs-Neutronenquelle Heinz Meier-Leibnitz (FRM II) is actively participating in the worldwide efforts on developing high-density uranium fuels in order to reduce the enrichment of fuels used in high flux research reactors. This work is part of a parameter study to define possible compatible FRM II core designs for conversion. As a first step, a code-to-code verification is performed and experimental data is used for validation. The Gambill experiment was performed in the early 1960’s in support of the HFIR program and provides results regarding the heat transfer coefficient and friction factors of water flowing through an electrically heated thin rectangular channel. A comparison is made between the Gambill Test and the results simulated by Ansys CFX and STAR-CCM+.

Improvement of RELAP5 code for density wave instability analysis in parallel narrow rectangular channels

As one of the most common types of oscillatory instability, density wave oscillation (DWO) is of practical importance in the general analysis of two-phase boiling systems. Due to the confinement effect of narrow space, the two-phase phenomena in thin rectangular channels are probably different from those in conventional pipes with large diameters. As the widely accepted system analysis code, RELAP5 has the capability to simulate the DWO phenomena in narrow channels, but the accuracy is limited under the condition of different pressures, flow rates, or subcoolings. In this paper, modifications for related constitutive models are proposed based on single-variable sensitivity analysis. Two-phase friction model and nucleate boiling heat transfer model are selected as the most effective models to improve the predictability of RELAP5. The influence of both models mentioned above is analyzed and it reveals that they are related to two-phase pressure drop and the vapor void fraction distribution along the channel, respectively. The modified calculation is assessed against the experimental results under the wide range of pressure 1–10 MPa, and these comparisons are performed in the map of stability boundary with two dimensionless parameters, phase change number Npch and subcooling number Nsub. Then the heating power and the period of flow oscillation under threshold condition are assessed in detail. The results show that a better agreement can be obtained between the modified calculations and the measured experimental data.

A predictive model for spiral wound reverse osmosis membrane modules: The effect of winding geometry and accurate geometric details

Abstract A new one-dimensional predictive model for spiral wound modules (SWMs) applied to reverse osmosis membrane systems is developed by incorporating a detailed description of the geometric features of SWMs and considering flow in two directions. The proposed model is found to capture existing experimental data well, with similar accuracy to the widely-used plate model in which the SWM is assumed to consist of multiple thin rectangular channels. However, physical parameters that should in principle be model-independent, such as membrane permeability, are found to differ significantly depending on which model is used, when the same data sets are used for parameter estimation. Conversely, when using the same physical parameter values in both models, the water recovery predicted by the plate-like model is 12–20% higher than that predicted by the spiral model. This discrepancy is due to differences in the description of geometric features, in particular the active membrane area and the variable channel heights through the module, which impact on predicted performance and energy consumption. A number of design variables – the number of membrane leaves, membrane dimensions, centre pipe radius and the height of feed and permeate channels – are varied and their effects on performance, energy consumption and calculated module size are analysed. The proposed spiral model provides valuable insights into the effects of complex geometry on the performance of the SWM as well as of the overall system, at a low computational cost.

A critical heat flux experiment with water flow at low pressures in thin rectangular channels

Experimental investigation was performed on the critical heat flux (CHF) in thin rectangular channels with very wide mass velocity range at low pressures. Different test sections were adopted with the different heated length and heated width. Both the vertical upward flow and downward flow were tested during the experiment. The results prove that the effect of the heated length on the CHF exists in the high mass velocity test but it is not very strong. The CHF rises with shorter heated length. At low mass velocities, the CHF at downward flow is much lower than that at upward flow. Empirical correlations were compared with the experimental data both from present and others’ studies. Empirical correlations provided by Katto and Gambill gave out good prediction for the low upflow and the high downflow respectively. The Sudo correlation had wide flow range but it overestimated at low mass velocity and underestimated at high mass velocity. A new CHF correlation for the large flow rate shows good agreement with the present and others’ studies. High pressure drop was found in the experiment at high flow rate conditions. It was analyzed and discussed in the paper.

Magnetic separation of algae genetically modified for increased intracellular iron uptake.

Algae were investigated in the past as a potential source of biofuel and other useful chemical derivatives. Magnetic separation of algae by iron oxide nanoparticle binding to cells has been proposed by others for dewatering of cellular mass prior to lipid extraction. We have investigated feasibility of magnetic separation based on the presence of natural iron stores in the cell, such as the ferritin in Auxenochlorella protothecoides (A. p.) strains. The A. p. cell constructs were tested for inserted genes and for increased intracellular iron concentration by inductively coupled plasma atomic absorption (ICP-AA). They were grown in Sueoka's modified high salt media with added vitamin B1 and increasing concentration of soluble iron compound (FeCl3 EDTA, from 1× to 8× compared to baseline). The cell magnetic separation conditions were tested using a thin rectangular flow channel pressed against interpolar gaps of a permanent magnet forming a separation system of a well-defined fluid flow and magnetic fringing field geometry (up to 2.2 T and 1,000 T/m) dubbed "magnetic deposition microscopy", or MDM. The presence of magnetic cells in suspension was detected by formation of characteristic deposition bands at the edges of the magnet interpolar gaps, amenable to optical scanning and microscopic examination. The results demonstrated increasing cellular Fe uptake with increasing Fe concentration in the culture media in wild type strain and in selected genetically-modified constructs, leading to magnetic separation without magnetic particle binding. The throughput in this study is not sufficient for an economical scale harvest.

High-frame rate imaging of two-phase flow in a thin rectangular channel using fast neutrons

We have demonstrated the feasibility of performing high-frame-rate, fast neutron radiography of air–water two-phase flows in a thin channel with rectangular cross section. The experiments have been carried out at the accelerator facility of the Physikalisch-Technische Bundesanstalt. A polychromatic, high-intensity fast neutron beam with average energy of 6MeV was produced by 11.5MeV deuterons hitting a thick Be target. Image sequences down to 10ms exposure times were obtained using a fast-neutron imaging detector developed in the context of fast-neutron resonance imaging. Different two-phase flow regimes such as bubbly slug and churn flows have been examined. Two phase flow parameters like the volumetric gas fraction, bubble size and mean bubble velocities have been measured. The first results are promising, improvements for future experiments are also discussed.

대용량 중력장 SPLITT Fractionation: 분획효율에 미치는 채널 두께와 유속의 영향

SPLITT fractionation (SF) allows continuous (and thus a preparative scale) separation of micron- sized particles into two size fractions ('fraction-a' and 'fraction-b'). SF is usually carried out in a thin rectangular channel with two inlets and two outlets, which is equipped with flow stream splitters at the inlet and the outlet of the channel, respectively. A new large scale splitter-less gravitational SF (GSF) system had been assembled, which was designed to eliminate the flow stream splitters and thus is operated by the full feed depletion (FFD) mode (FFD-GSF). In the FFD mode, there is only one inlet through which the sample is fed. There is no carrier liquid fed into the channel, and thus prevents the sample dilution. The effects of the sample-feeding flow rate, the channel thickness on the fractionation efficiency (FE, number % of particles that have the size predicted by theory) of FFD-GSF was investigated using industrial polyurethane (PU) latex beads. The carrier liquid was water containing 0.1% FL-70 (particle dispersing agent) and 0.02% sodium azide (used as bactericide). The sample loading rate was varied from about 4 to 7 L/hr with the sample concentration fixed at 0.01%. The GSF channel thickness was varied from 900 to 1300 µm. Particles exiting the GSF channel were collected and monitored by optical microscopy (OM). Sample recovery was monitored by collecting the fractionated particles on a 0.45 µm membrane filter. It was found that FE of fraction-a was increased as the channel thickness increases, and FE of fraction-b was increased as the flow rate was increased. In all cases, the sample recovery has higher than 95%. It seems the new splitter-less FFD GSF system could become a useful tool for large scale separations of various types of micron-sized particles. 요약 : SPLITT 분획법(Split-flow thin cell fractionation, SF)은 입자성 물질이나 거대분자를 크기에

Effect of Sample-loading on Fractionation Efficiency (FE) in a Large Scale Splitter-less Gravitational SPLITT Fractionation (GSF)

Gravitational SPLITT fractionation (GSF) provides separation of colloidal particles into two subpopulations in a preparative scale. Conventionally, GSF is carried out in a thin rectangular channel having two inlets and two outlets at the top and bottom of the channel, respectively. And the channel is equipped with two flow-splitters, one between the top and bottom inlets and another between the top and bottom outlets. A large scale splitter-less GSF system had been developed, which was designed to operate in the full feed depletion (FFD) mode. In the FFD mode, there is only one inlet through which the sample is fed, thus preventing the sample dilution. In this study, the effect of the sample-loading (in the unit of g/hr) on the fractionation efficiency (FE, number% of particles in a GSF fraction that have the sizes expected by theory) of the new large scale splitter-less FFD-GSF system was investigated. The system was tested in the sample-loading range of 3.0-12.0 g/hr with polyurethane latex beads (PU) and sea-sediment. It was found that there is an optimum range in the sample-loading for a FFD-GSF separation. It was also found that there is a general tendency of FE decreasing as the concentration of the sample suspension increases.

Electric field enhanced gel controlled cross-flow ultrafiltration under turbulent flow conditions

A theoretical analysis based on integral method for quantification of the permeate flux and mass transfer coefficient in gel layer controlled electric field enhanced cross-flow ultrafiltration considering developing mass transfer boundary layer under turbulent flow regimes is elaborated in the present work. Thin rectangular channel and tubular module are selected as system geometry. The analysis for tubular module is carried out for the experimental data of colloidal solution of gelatin available in the literature [H. Yukawa, K. Shimura, A. Maniwa, Cross flow electro-ultrafiltration for colloidal solution of protein, J. Chem. Eng. Jpn. 16 (4) (1983) 305–311]. In rectangular channel, ultrafiltration experiments for turbulent flow conditions are investigated using synthetic juice (a mixture of pectin and sucrose) with a 50 kDa flat sheet polyethersulfone membrane. Furthermore, a parametric study has been carried out to observe the effects of operating conditions such as electric field, feed concentration, cross-flow velocity etc., on the permeate flux. Experimental results show a significant enhancement in permeate flux with the application of a suitable dc electric field. Model predicted results are successfully compared with the experimental data. Effects of d.c. electric field on the variation of permeate flux along the length of the module are also quantified using the model.

Correlation for Flow Boiling Critical Heat Flux in Thin Rectangular Channels

The effect of heated length on critical heat flux (CHF) in thin rectangular channels under atmospheric pressure has been studied. CHF in small channels has been widely studied in the last decades but most of the studies are based on flow in round tubes and number of studies focused on rectangular channels is relatively small. Although basic triggering mechanisms, which lead to CHF in thin rectangular channels, are similar to that of tubes, applicability of thermal hydraulic correlations developed for tubes to rectangular channels are questionable since heat transfer in rectangular channels are affected by the existence of nonheated walls and the noncircular geometry of channel circumference. Several studies of CHF in thin rectangular channels have been reported in relation to thermal hydraulic design of research reactors and neutron source targets and correlations have been proposed, but the studies mostly focus on geometrical conditions of the application of interest and therefore effect of channel parameters exceeding their interest is not fully understood. In his study, CHF data for thin rectangular channels have been collected from previous studies and the effect of heated length on CHF was examined. Existing correlations were verified with data with positive quality outlet flow but none of the correlations successfully reproduced the data for a wide range of heated lengths. A new CHF correlation for quality region applicable to a wide range of heated lengths has been developed based on the collected data.

Experimental research on heat transfer of natural convection in vertical rectangular channels with large aspect ratio

This work presents the experimental research on the steady laminar natural convection heat transfer of air in three vertical thin rectangular channels with different gap clearance. The much higher ratio of width to gap clearance (60–24) and the ratio of length to gap clearance (800–320) make the rectangular channels similar with the coolant flow passage in plate type fuel reactors. The vertical rectangular channels were composed of two stainless steal plates and were heated by electrical heating rods. The wall temperatures were detected with the K-type thermocouples which were inserted into the blind holes drilled in the steal plates. Also the air temperatures at the inlet and outlet of the channel were detected. The wall heat fluxes added to the air flow were calculated by the Fourier heat conduction law. The heat transfer characteristics were analyzed, and the average Nusselt numbers in all the three channels could be well correlated with the Rayleigh number or the modified Rayleigh number in a uniform correlation. Furthermore, the maximum wall temperatures were investigated, which is a key parameter for the fuel’s integrity during some accidents. It was found that even the wall heat flux was up to 1500 W/m 2, the maximum wall temperature was lower than 350 °C. All this work is valuable for the plate type reactor’s design and safety analysis.

Prediction of permeate flux during electric field enhanced cross-flow ultrafiltration—A neural network approach

Electric field enhanced cross flow ultrafiltration of aqueous solution of bovine serum albumin (BSA) has been carried out in a thin rectangular channel using 30,000 molecular weight cut-off membrane over a wide range of operating conditions. Detailed parametric study has been performed to observe the effect of feed concentration, electric field, cross flow velocity and pressure on permeate flux. An artificial neural network approach with single hidden layer has been systematically developed to predict permeate flux using some of the experimental results. The rest of the experimental results are successfully compared with the model predictions with less than 1% average error. The analysis reveals significant beneficial effect of electric field on permeate flux. In this work, emphasis has been given on random selection of training data and small network. The developed trained network is also able to capture the non-linear prediction of permeate flux with new operating conditions which has not been used in the training process and enhances the physical understanding of the process.

A new critical heat flux correlation for vertical water flow through multiple thin rectangular channels

A critical heat flux (CHF) study of the vertical up-flow of water through multiple thin rectangular channels was conducted. Pressures varied from 89.8 to 115 kPa, inlet temperatures from 291 to 306 K, and mass fluxes from 9.5 to 39 kg m −2 s −1. Electrical resistance heaters embedded in aluminum provided a uniform heat flux. A more universal and robust CHF correlation based on the geometry of the Advanced Test Reactor at Idaho National Laboratory was developed. This new CHF correlation predicts 126 data points from this and three previous studies within an error of ±8.5% with a 95% confidence.

ICONE15-10272 Critical Heat Flux correlation for thin rectangular channels

The effect of heated length on Critical heat flux (CHF) in thin rectangular channels was studied based on CHF data obtained under atmospheric pressure. CHF in small channels has been widely studied in the past decades but most of the studies are related to CHF in round tubes. Although basic mechanisms of burnout in thin rectangular channels are similar to tubes, applicability of CHF correlations for tubes to rectangular channels are questionable since CHF in rectangular channels are affected by the existence of non-heated walls and the non-circular geometry of channel circumference. Several studies of CHF in thin rectangular channels have been reported in relation to thermal hydraulic design of research reactors and neutron source targets and CHF correlations have been proposed, but the studies mostly focus on CHFs under geometrical conditions of the application of interest. In his study, existing CHF data obtained in thin rectangular channels were collected and the effect of heated length on CHF was examined. Existing CHF correlations were verified with positive quality flow CHF data but none of the correlations successfully reproduced the CHF for a wide range of heated length. A new CHF correlation for quality region applicable to a wide range of heated length was developed based on the collected data.

Prediction of the critical heat flux in annular regime in various vertical channels

The axial variation of film flow rate in annular regime was analyzed to predict the critical heat flux in water saturated flow boiling in various vertical channels. In the analyses, several quantities including the deposition and entrainment rates of droplets were evaluated with the correlations that were based on the separate experimental data of film flow rate and droplet flow rate in annular flow; model closure was achieved without introducing arbitrary constants. The predicted results were compared with extensive data of critical heat flux in flow boiling. Fairly good agreements were observed for the critical heat fluxes in round tubes with uniform and axially non-uniform heating and in non-circular shaped channels without sharp corners. It is hence expected that the important processes for the onset of critical heat flux condition in annular regime were satisfactorily described in the model. However, the critical heat fluxes were generally overestimated in thin rectangular channels with sharp corners. The non-uniform distribution of liquid film in channel cross-section would be the primary reason of the disagreement.