Range Of Low Flow Rates Research Articles

미세 소염소자를 포함하는 역화방지장치 내 공기 유동의 전산 해석

The relation between flow rate and pressure drop was investigated numerically for a flame arrester with a crimped ribbon element. Permeability and inertial/viscous resistance factor of the micro-scaled element were obtained from a laminar simulation. Then, the porous zone model was adopted to simulate the flow in a flame arrester. The simulation results of the pressure drop were in good agreement with the experimental in the low flow-rate range. The analysis process developed in this study can be extended to different configurations/shapes of flame arresters and working fluids such as hydrogen.

Regulating the Flow-Driven Translocation of Macromolecules through Nanochannels by Interfacial Physical Adsorption

By using a model system composed of an anodic aluminum oxide nanopore (AAO), poly(benzyl acrylate) (PBAN) adsorbent, and polystyrene (PSN) probe, where N represents the degree of polymerization, this work has explored how the physical adsorption of PBA onto the surface of the AAO nanopore (rp ≈ 10 nm) influences the flow-driven translocation of PS in toluene. In the low flow rate range (Q = 0.02 mL/h), the translocation of PS chains is purely diffusive, and the partially reversible adsorption behavior of PBAN is observed only when N < ∼360, showing a strong chain length dependence. In the partially reversible regime, the interfacial thickness (δ) of the adsorption layer is estimated to be from ∼1.5 to ∼2.9 nm depending on the chain length. In the mixed solutions, when N increases from 0 to 75 and 150 for PBAN, the cut-off size (COS) of the membrane for broadly distributed PSB-285K (Mw/Mn ≈ 2.48) is estimated to decrease from ∼10.0 to ∼8.0 and ∼6.0 nm, respectively; in addition, the introduction of PBA360 can promote the separation of narrowly distributed PS655 and PS1200 by regulating re, whereas in the high flow rate range (Q > 0.02 mL/h), the translocation for PS long chains is based on the mechanism of molecular deformation, and the flow rate-dependent translocation shows a strong dependence on the chain length of PBAN. Namely, in mixed solutions, when N increases from 150 to 360, the critical flow rate (Qc) is found to slightly increase from ∼0.30 to ∼0.45 mL/h for PS1500 translocation; in addition, the cut-off performance of PSB-285K displays dependence both on flow rate and PBAN chain length. Our result has demonstrated a novel strategy to regulate the cut-off performance during the translocation of (bio)macromolecules through nanopores via partially reversible interfacial physical adsorption.

A pore-scale study for reactive transport processes in double-layer gradient electrode as negative side of a deep eutectic solvent electrolyte-based vanadium-iron redox flow battery

Porous electrodes are critical component of redox flow batteries (RFBs), that decide the fluid, species/charge transport and electrochemical reaction properties during the operation of RFBs. It is a potential way to elevate the performance of RFBs by applying the porous electrodes with gradient pore structures. However, it is still lack of a suitable numerical model to understand the reactive transport processes in the heterogeneous pore structures, thus to design and develop the optimal RFB electrodes. Using a lattice Boltzmann model, this work studies the pore-scale reactive transfer behaviors in a double-layer gradient electrode assembling as the negative side of deep eutectic solvents electrolyte-based vanadium-iron RFB, that consists of a graphite felt near the current collector side and a carbon paper near the membrane side. The numerical results reveal the galvanostatic discharging performance of double-layer electrode under the different electrolyte feeding modes and flow rates. Comparing with full flow-through feeding mode, the interdigitated flow feeding mode would give rise to serious inhomogeneity of electrolyte flowing at the low flow rate condition, thereby resulting in the sluggish convective mass transfer performance near the membrane side. Moreover, the total power loss of double-layer electrode is higher than that of the mono-layer carbon paper electrode within the low flow rate range. Conversely, the double-layer electrode with interdigitated flow mode can achieve the lowest total power loss than mono-layer electrodes at the high inlet flow rate. This work provides a new pathway to investigate the RFB power performance effected by the gradient porous structures of electrodes.

Final report on supplementary comparison of national standards for liquid flow COOMET.M.FF-S2 (COOMET Project 406/UA/07)

A supplementary comparison, COOMET.M.FF-S2, in the field of water flow was organized by the COOMET Technical Committee (TC) 1.4 Flow Measurement. The goal of the comparison was to confirm the calibration and measurement capabilities (CMC) of the participating national metrology institutes (NMIs) in the flow ranges between 0.5 m3/h and 5.0 m3/h, and, respectively, between 20.0 m3/h and 100.0 m3/h. This is the first comparison in the field of fluid flow which has been done by the COOMET TC Flow Measurement.This report describes the comparison results of the following water flow facilities (NMIs): PTB (Braunschweig, Germany), National standards Centre of the Republic of Uzbekistan (Tashkent, Republic of Uzbekistan), LEI (Kaunas, Lithuania), SMU (Bratislava, Slovakia), BelGIM (Minsk, Belarus), VNIIR (Kazan, Russia).The PTB was designated as the pilot lab of this comparison, due to the low measurement uncertainty of its water flow primary standard, in comparison to all participants, and because of its experience in leading and participating in previous international flow comparisons.In order to cover a large flowrate range, two transfer standard packages were delivered to all involved NMIs of the inter-laboratory comparison. For low flowrate range and nominal diameter of 25 mm a turbine meter and an electromagnetic flowmeter were used as transfer standards. For upper flow rates two turbine meters with a nominal diameter of 80 mm were used. All calibrations were made during March 2009 until May 2012.Main textTo reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

전산유체역학 정보 기반 스풀변위보상 저유량대역 정밀제어에 관한 실험적 연구

전산유체역학 정보 기반 스풀변위보상 저유량대역 정밀제어에 관한 실험적 연구

Inter-Blade Vortex and Vortex Rope Characteristics of a Pump-Turbine in Turbine Mode under Low Flow Rate Conditions

Pump-turbines are often used to provide a stable power supply with a constant frequency in response to intermittent renewable energy resources. However, existing pumped-storage power stations often operate under off-design conditions because of the increasing amounts of inconsistent renewable resources that have been added to the grid. Under off-design low flow rate conditions, inter-blade vortex and vortex rope phenomena usually develop in the runner and draft tube passages, respectively, in turbine mode. These vortices cause complicated flow patterns and pressure fluctuations that destabilize the operation of the pump-turbine system. Therefore, this study investigates the influence of correlation between the inter-blade vortex and vortex rope phenomena under low flow rate conditions. Three-dimensional steady- and unsteady-state Reynolds-averaged Navier–Stokes equations were calculated with a two-phase flow analysis using a shear stress transport as the turbulence model. The inter-blade vortices in the runner passages were captured well at the low flow rate conditions, and the vortex rope was found to develop within a specific range of low flow rates. These vortex regions showed a blockage effect and complicated flow characteristics with backflow in the passages. Moreover, higher unsteady pressure characteristics occurred at locations where the vortices were especially pronounced.

Hydrodynamic Resistance of Intracranial Flow-Diverter Stents: Measurement Description and Data Evaluation

PurposeIntracranial aneurysms are malformations forming bulges on the walls of brain arteries. A flow diverter device is a fine braided wire structure used for the endovascular treatment of brain aneurysms. This work presents a rig and a protocol for the measurement of the hydrodynamic resistance of flow diverter stents. Hydrodynamic resistance is interpreted here as the pressure loss versus volumetric flow rate function through the mesh structure. The difficulty of the measurement is the very low flow rate range and the extreme sensitivity to contamination and disturbances.MethodsRigorous attention was paid to reproducibility, hence a strict protocol was designed to ensure controlled circumstances and accuracy. Somewhat unusually, the history of the development of the rig, including the pitfalls was included in the paper. In addition to the hydrodynamic resistance measurements, the geometrical properties—metallic surface area, pore density, deployed and unconstrained length and diameter—of the stent deployment were measured.ResultsBased on our evaluation method a confidence band can be determined for a given deployment scenario. Collectively analysing the hydrodynamic resistance and the geometric indices, a deeper understanding of an implantation can be obtained. Our results suggest that to correctly interpret the hydrodynamic resistance of a scenario, the deployment length has to be considered. To demonstrate the applicability of the measurement, as a pilot study the results of four intracranial flow diverter stents of two types and sizes have been reported in this work. The results of these measurements even on this small sample size provide valuable information on differences between stent types and deployment scenarios.

Prediction of oil flow rate through an orifice flow meter: Artificial intelligence alternatives compared

Fluid-flow measurements of petroleum can be performed using a variety of equipment such as orifice meters and wellhead chokes. It is useful to understand the relationship between flow rate through orifice meters (Qv) and the five fluid-flow influencing input variables: pressure (P), temperature (T), viscosity (μ), square root of differential pressure (ΔP^0.5), and oil specific gravity (SG). Here we evaluate these relationships using a range of machine-learning algorithms applied to orifice meter data from a pipeline flowing from the Cheshmeh Khosh Iranian oil field. Correlation coefficients indicate that (Qv) has weak to moderate positive correlations with T, P, and μ, a strong positive correlation with the ΔP^0.5, and a weak negative correlation with oil specific gravity. In order to predict the flow rate with reliable accuracy, five machine-learning algorithms are applied to a dataset of 1037 data records (830 used for algorithm training; 207 used for testing) with the full input variable values for the data set provided. The algorithms evaluated are: Adaptive Neuro Fuzzy Inference System (ANFIS), Least Squares Support Vector Machine (LSSVM), Radial Basis Function (RBF), Multilayer Perceptron (MLP), and Gene expression programming (GEP). The prediction performance analysis reveals that all of the applied methods provide predictions at acceptable levels of accuracy. The MLP algorithm achieves the most accurate predictions of orifice meter flow rates for the dataset studied. GEP and RBF also achieve high levels of accuracy. ANFIS and LSSVM perform less well, particularly in the lower flow rate range (i.e., <40,000 stb/day). Some machine learning algorithms have the potential to overcome the limitations of idealized streamline analysis applying the Bernoulli equation when predicting flow rate across an orifice meter, particularly at low flow rates and in turbulent flow conditions. Further studies on additional datasets are required to confirm this.

Impact of guide vane opening angle on the flow stability in a pump-turbine in pump mode

In the pump mode (storage mode) of a pump-turbine, unstable head variations occur as the flow rate decreases, leading to unstable, unsafe operation. Thus, the hydrodynamics of pump-turbines in the unstable operating range should be investigated to improve their designs. This study presents experimental and numerical studies of the hydrodynamics. The experiments investigated the external characteristics with the head instabilities captured by both the model tests and the computational fluid dynamics simulations. The computational fluid dynamics model used detached eddy simulations to study the flow details which showed that hydraulic losses were the reason for the unstable head variations and the poor flow regime was the source of the losses. In the unstable, low flow rate range, the flow direction is no longer consistent with the guide vane direction, so undesirable flow structures develop in the passages. Therefore, appropriate guide vane opening angles are needed to improve the flow regime and reduce the hydraulic losses. These will enhance the operating stability and safety in engineering applications.

An ultra high-pressure test rig for measurements of small flow rates with different viscosities

Within the framework of a research project regarding investigations on a high-pressure Coriolis mass flow meter (CMF) a portable flow test rig for traceable calibration measurements of the flow rate (mass - and volume flow) in a range of 5gmin−1 to 500gmin−1 and in a pressure range of 0.1MPa to 85MPa was developed. The measurement principle of the flow test rig is based on the gravimetrical measuring procedure with flying-start-and-stop operating mode. Particular attention has been paid to the challenges of temperature stability during the measurements since the temperature has a direct influence on the viscosity and flow rate of the test medium. For that reason the pipes on the high-pressure side are double-walled and insulated and the device under test (DUT) has an enclosure with a separate temperature control. From the analysis of the first measurement with tap water at a temperature of 20°C and a pressure of 82.7MPa an extensive uncertainty analysis has been carried out. It was found that the diverter (mainly due to its asymmetric behaviour) is the largest influence factor on the total uncertainty budget. After a number of improvements, especially concerning the diverter, the flow test rig has currently an expanded measurement uncertainty of around 1.0% in the lower flow rate range (25gmin−1) and 0.25% in the higher flow rate range (400gmin−1) for the measurement of mass flow. Additional calibration measurements with the new, redesigned flow test rig and highly viscous base oils also indicated a good agreement with the theoretical behaviour of the flow meter according to the manufacturers׳ specifications with water as test medium. Further improvements are envisaged in the future in order to focus also on other areas of interest.

Numerical and Experimental Analysis of Flow Phenomena in a Centrifugal Pump Operating Under Low Flow Rates

The characteristics of flow instabilities as well as the cavitation phenomenon in a centrifugal pump operating at low flow rates were studied by experimental and numerical means, respectively. Specially, a three-dimensional (3D) numerical model of cavitation was applied to simulate the internal flow through the pump and suitably long portions of the inlet and outlet ducts. As expected, cavitation proved to occur over a wide range of low flow rates, producing a characteristic creeping shape of the head-drop curve and developing in the form of nonaxisymmetric cavities. As expected, the occurrence of these cavities, attached to the blade suction sides, was found to depend on the pump's flow coefficient and cavitation number. The experiments focused on the flow visualization of the internal flow patterns by means of high-speed digital movies and in the analysis of the inlet pressure pulsations near the impeller eye by means of fast response pressure transducers. The experimental results showed that the unsteady behavior of the internal flow in the centrifugal pump operating at low flow rates has the characteristics of a peculiar low-frequency oscillation. Meanwhile, under certain conditions, the low-frequency pressure fluctuations were closely correlated to the flow instabilities induced by the occurrence of cavitation phenomena at low flow rates. Finally, the hydraulic performances of the centrifugal pump predicted by numerical simulations were in good agreement with the corresponding experimental data.

Flow enhancement in pulsating flow of non-colloidal suspensions in tubes

The flow enhancement of non-colloidal suspensions in pulsating flow is experimentally investigated. At low flow-rate range, a flow enhancement of up to 10% was observed due to the shear thinning of viscosity, while a slightly negative flow enhancement can be observed at high flow-rate range, maybe due to the Newtonian plus a slight amount of shear thickening nature of the suspension at high shear rates. At low flow rates, the flow enhancement is found to be insensitive to the mean pressure gradient.

Effect of H2 Flow Rate on High-Rate Etching of Si by Narrow-Gap Microwave Hydrogen Plasma

For the purpose of realizing a low-cost production process of silane (SiH4) gas, we have proposed the high-rate etching of metallurgical-grade Si by narrow-gap microwave hydrogen plasma. In this paper, effect of hydrogen gas flow rate (0–10 L/min) on the etch rate has been investigated and correlated with the relative variation of hydrogen-atom density estimated by actinometry. By decreasing hydrogen gas flow rate, the etch rate gradually increases up to the maximum value of 11 μm/min at 2 L/min. This increase is well correlated with the increase of hydrogen-atom density due to the longer residence time of hydrogen molecules in the plasma. On the other hand, when the gas flow rate is lower than 2 L/min, the etch rate abruptly decreases with decreasing gas flow rate in spite of the increase of hydrogen-atom density. From the surface observations and Raman measurements, it is found that the decrease in etch rate in the lower flow rate range is attributed to the formation of microcrystalline Si particles due to the decomposition of generated-SiH4 molecules in the plasma.

Effect of growth gas flow rate on the SiC crystal resistivity

Abstract

Optimisation of dual purging location for better mixing in ladle: a water model study

Mixing time studies were performed on a one-fifth scale aqueous model of a single tapered ladle with different bottom purging locations. Two porous plugs were used simultaneously to purge compressed air as an analogue to argon and this was referred as dual purging. KCl solution (1 N) was used as the tracer for measuring mixing time. The scaled down gas flowrate varied from 10 to 80 L m–1. Around 400 experiments were done including all possible dual purging locations and the location which gives least mixing time was identified. The results were compared with corresponding single purging experiments and it was found that dual purging can reduce mixing time to a great extent even in the lower flowrate range and a location better than ±R/2 has been suggested. Effect of differential flow on mixing time has also been reported.

Numerical and experimental mixing studies in a MEMS-based multilaminated/elongational flow micromixer

Improvement of mixing quality in microchannel mixers or reactors has been recognized as a relevant technical issue critical to the development and application of integrated microchemical processing systems. Silicon micro- electro mechanical systems (MEMS) technology was successfully used to fabricate a novel multichannel micromixer. This improved micromixer design basically used the mechanisms of fluid multilamination, elongational flow, and geometric focusing for mixing enhancement. The fabricated triple-stack (Pyrex™/silicon/Pyrex™) multilaminated/elongational flow micromixer (herein referred to as MEFM-4) was evaluated for its mixing performance using residence time distribution (RTD) measure in conjunction with UV–vis absorption spectroscopy detection technique. Using a semi-empirical model and the so-called convolution–deconvolution theorem, a model description of the experimental RTD data was obtained for the flow/mixing unit. This result was compared with numerical RTD predictions based on computational fluid dynamics (CFD) simulations. The simulation results are in good agreement with the experimental data, especially in the low flow-rate range (Reynolds number <13 in this study). However, as expected, the accuracy of the CFD simulations is generally limited at higher flow rates (high Peclet number) because of unavoidable numerical diffusion. This paper describes the efficient design, fabrication and characterization of an effective microchannel mixer for microchemical systems’ applications.

Application of hilbert-huang transform to denoising in vortex flowmeter

Due to piping vibration, fluid pulsation and other environmental disturbances, variations of amplitude and frequency to the raw signals of vortex flowmeter are imposed. It is difficult to extract vortex frequencies which indicate volumetric flowrate from noisy data, especially at low flowrates. Hilbert-Huang transform was adopted to estimate vortex frequency. The noisy raw signal was decomposed into different intrinsic modes by empirical mode decomposition, the time-frequency characteristics of each mode were analyzed, and the vortex frequency was obtained by calculating partial mode’s instantaneous frequency. Experimental results show that the proposed method can estimate the vortex frequency with less than 2% relative error; and in the low flowrate range studied, the denoising ability of Hilbert-Huang transform is markedly better than Fourier based algorithms. These findings reveal that this method is accurate for vortex signal processing and at the same time has strong anti-disturbance ability.

Development of a Positive Displacement Micro-Hydro Turbine

The objective of this study is to develop an efficient turbine that can be used to extract micro hydropower potential of a water supply system. For the case of high head and critical low flow rate range of micro hydropower resources, it requires very low specific speed turbines which are lower than conventional impulse turbines’ specific speed. For this purpose, we develop a new Positive Displacement Turbine (PDT). In order to reveal the performance characteristics of the new turbine, one conventional impulse turbine, which is used for automatic water faucet system, was tested for comparison. The test results show that the PDT was much more efficient than a conventional turbine and it can sustain high efficiency under the wide range of operating conditions. In addition, the efficiency of the PDT is much improved when reducing its side clearance. The pressure pulsations at the inlet and outlet of the PDT can be considerably minimized by using simple dampers.

The foam/emulsion analogy in structure and drainage.

The often quoted analogy between foams and emulsions is experimentally tested by studying properties after settling and under forced drainage of oil-in-water emulsions of drop size similar as for bubbles generally used in foam experiments. Observations with regard to structure, water fraction and drainage wave properties confirm the expected similarity in the low flow rate range. However, while for foams a convective circulation on the scale of the container sets in for values of water fraction exceeding about 0.2, no such convection is found in emulsions. Here instabilities are only encountered at water fractions of about 0.4, close to the void fraction of random packings of spheres. These take on the form of descending pulses of increased water fraction and lead to the transition from a frozen to a locally agitated structure.

High flux boiling in low flow rate, low pressure drop mini-channel and micro-channel heat sinks

Due to the need for practical cooling technologies which could dissipate high heat fluxes, an experimental study of pressure drop and CHF in mini-channel ( D = 2.54 mm) and micro-channel ( D = 510 μm) heat sinks of 1 cm heated length was performed using R-113. Test conditions included inlet subcooling ranging from 10 to 32°C and a range of low flow rates up to a maximum of 95 ml min −1. The tests yielded CHF values for both heat sinks in excess of 200 W cm −2 with the advantage of both low flow rates and low pressure drops ( ΔP < 0.32 bar) as compared to high-flux, single-phase micro-channel heat sinks. Key features of the miniature heat sinks include a lack of inlet subcooling effect on CHF and superheated outlet conditions at the lowest flow rates. A single CHF correlation was developed for both heat sinks. The paper will illustrate the use of the CHF correlation and a generalized model for pressure drop as predictive tools in assessing the merits of different channel sizes in incorporating miniature heat sink technology into high heat flux cooling schemes. Overall, the mini-channel's performance proved superior to the micro-channel due to pressure drops less than 0.01 bar for comparable CHF values as well as the reduced likelihood of clogging and the relative ease in fabricating the mini-channel.